1. Install git and maven
$ sudo apt-get install git
$ sudo apt-get install maven

2. Create jetty project directory
$ mkdir jetty-9.1
$ cd jetty-9.1

3 Checkout release-9.1 branch from github
git clone git://git.eclipse.org/gitroot/jetty/org.eclipse.jetty.project.git -b release-9.1

4. Edit the maven settings.xml file. Set the maven local repository.
   If you are using a proxy to access the Internet set also the proxy properties.

settings>
  <localRepository>~/.m2</localRepository>
  <interactiveMode>true</interactiveMode>
  <offline>false</offline>
  <proxies>
  <!--
   <proxy>
      <active>true</active>
      <protocol>http</protocol>
      <host>proxy.eclipse.org</host>
      <port>9898</port>
    </proxy>
  -->
  </proxies>
  <mirrors>
    <mirror>
      <id>central</id>
      <name>central</name>
      <url>http://repo2.maven.org/maven2/</url>
      <mirrorOf>*</mirrorOf>
    </mirror>
  </mirrors>
</settings>

5. Build jetty project
$ mvn clean install

Here is the result summary of the build:

[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO] 
[INFO] Jetty :: Project .................................. SUCCESS [56.365s]
[INFO] Jetty :: Utilities ................................ SUCCESS [1:27.998s]
[INFO] Jetty :: Http Utility ............................. SUCCESS [3.250s]
[INFO] Jetty :: IO Utility ............................... SUCCESS [48.943s]
[INFO] Jetty :: XML utilities ............................ SUCCESS [1.909s]
[INFO] Jetty :: JMX Management ........................... SUCCESS [8.247s]
[INFO] Jetty :: Server Core .............................. SUCCESS [2:50.180s]
[INFO] Jetty :: Security ................................. SUCCESS [11.588s]
[INFO] Jetty :: Servlet Handling ......................... SUCCESS [8.644s]
[INFO] Jetty :: Webapp Application Support ............... SUCCESS [3.812s]
[INFO] Jetty :: JNDI Naming .............................. SUCCESS [5.024s]
[INFO] Jetty :: Plus ..................................... SUCCESS [3.779s]
[INFO] Jetty :: Servlet Annotations ...................... SUCCESS [5.598s]
[INFO] Jetty :: Ant Plugin ............................... SUCCESS [9.577s]
[INFO] Jetty :: Continuation ............................. SUCCESS [0.988s]
[INFO] Jetty :: SPDY :: Parent ........................... SUCCESS [1.490s]
[INFO] Jetty :: SPDY :: Core ............................. SUCCESS [8.192s]
[INFO] Jetty :: SPDY :: Client Binding ................... SUCCESS [3.632s]
[INFO] Jetty :: SPDY :: Server Binding ................... SUCCESS [40.980s]
[INFO] Jetty :: SPDY :: HTTP Common ...................... SUCCESS [0.562s]
[INFO] Jetty :: Asynchronous HTTP Client ................. SUCCESS [2:58.961s]
[INFO] Jetty :: Utility Servlets and Filters ............. SUCCESS [1:09.212s]
[INFO] Jetty :: SPDY :: HTTP Server ...................... SUCCESS [51.603s]
[INFO] Jetty :: SPDY :: HTTP Client Transport ............ SUCCESS [4.825s]
[INFO] Jetty :: JAAS ..................................... SUCCESS [1.133s]
[INFO] Jetty :: Websocket :: Parent ...................... SUCCESS [1.749s]
[INFO] Jetty :: Websocket :: API ......................... SUCCESS [7.984s]
[INFO] Jetty :: Websocket :: Common ...................... SUCCESS [12.236s]
[INFO] Jetty :: Websocket :: Client ...................... SUCCESS [30.133s]
[INFO] Jetty :: Websocket :: Servlet Interface ........... SUCCESS [5.433s]
[INFO] Jetty :: Websocket :: Server ...................... SUCCESS [25.249s]
[INFO] Jetty :: Websocket :: javax.websocket :: Client Implementation  SUCCESS [7.568s]
[INFO] Jetty :: Websocket :: javax.websocket.server :: Server Implementation  SUCCESS [8.913s]
[INFO] Jetty :: JSP dependencies ......................... SUCCESS [7.399s]
[INFO] Jetty :: Jetty Maven Plugin ....................... SUCCESS [26.288s]
[INFO] Jetty :: SPDY :: HTTP Web Application ............. SUCCESS [1.502s]
[INFO] Jetty :: Websocket :: Mux Extension ............... SUCCESS [3.406s]
[INFO] Jetty :: Utilities :: Ajax(JSON) .................. SUCCESS [1.805s]
[INFO] Jetty :: Jetty JSPC Maven Plugin .................. SUCCESS [7.305s]
[INFO] Jetty :: Deployers ................................ SUCCESS [25.999s]
[INFO] Jetty :: Start .................................... SUCCESS [3.326s]
[INFO] Example :: Jetty Spring ........................... SUCCESS [4.482s]
[INFO] Jetty :: Proxy .................................... SUCCESS [20.871s]
[INFO] Jetty :: JASPI Security ........................... SUCCESS [2.614s]
[INFO] Jetty :: OSGi ..................................... SUCCESS [0.019s]
[INFO] Jetty :: OSGi :: Boot ............................. SUCCESS [8.017s]
[INFO] Jetty :: OSGi :: Boot JSP ......................... SUCCESS [1.154s]
[INFO] Jetty :: OSGi :: Boot :: Warurl ................... SUCCESS [0.872s]
[INFO] Jetty :: OSGi NPN Fragment ........................ SUCCESS [0.626s]
[INFO] Jetty :: OSGi :: HttpService ...................... SUCCESS [1.924s]
[INFO] Jetty :: OSGi :: WebApp ........................... SUCCESS [0.725s]
[INFO] Jetty :: OSGi :: Context .......................... SUCCESS [0.718s]
[INFO] Jetty Tests :: Parent ............................. SUCCESS [0.014s]
[INFO] Jetty Tests :: WebApps :: Parent .................. SUCCESS [0.014s]
[INFO] Test :: Jetty Test Webapp ......................... SUCCESS [4.577s]
[INFO] Jetty :: OSGi :: Test ............................. SUCCESS [1:13.350s]
[INFO] Jetty :: Rewrite Handler .......................... SUCCESS [2.508s]
[INFO] Jetty Tests :: Sessions :: Parent ................. SUCCESS [0.015s]
[INFO] Jetty Tests :: Sessions :: Common ................. SUCCESS [1.678s]
[INFO] Jetty :: NoSQL Session Managers ................... SUCCESS [3.916s]
[INFO] Test :: Jetty Proxy Webapp ........................ SUCCESS [0.867s]
[INFO] Jetty Tests :: WebApp :: RFC2616 .................. SUCCESS [0.620s]
[INFO] Jetty Tests :: WebApp :: Mock Resources ........... SUCCESS [0.606s]
[INFO] Jetty Tests :: Spec Test WebApp :: Parent ......... SUCCESS [0.015s]
[INFO] Jetty Tests :: WebApp :: Servlet Spec :: Fragment Jar  SUCCESS [0.542s]
[INFO] Jetty Tests :: WebApp :: Servlet Spec :: ServletContainerInitializer Test Jar  SUCCESS [0.565s]
[INFO] Jetty Tests :: Webapps :: Spec Webapp ............. SUCCESS [4.491s]
[INFO] Jetty Tests :: WebApp :: JAAS ..................... SUCCESS [0.305s]
[INFO] Jetty Tests :: WebApp :: JNDI ..................... SUCCESS [0.662s]
[INFO] Jetty Tests :: Sessions :: Hash ................... SUCCESS [34.291s]
[INFO] Jetty Tests :: Sessions :: JDBC ................... SUCCESS [1:34.720s]
[INFO] Test :: Continuation .............................. SUCCESS [1.737s]
[INFO] Jetty Tests :: Login Service ...................... SUCCESS [8.810s]
[INFO] Jetty Examples :: Parent .......................... SUCCESS [0.013s]
[INFO] Example Async Rest ................................ SUCCESS [0.013s]
[INFO] Example Async Rest :: Jar ......................... SUCCESS [2.661s]
[INFO] Example Async Rest :: Webapp ...................... SUCCESS [0.597s]
[INFO] Example :: Jetty Embedded ......................... SUCCESS [2.116s]
[INFO] Jetty :: Monitoring ............................... SUCCESS [2:09.099s]
[INFO] Jetty :: Distribution Assemblies .................. SUCCESS [24.425s]
[INFO] Jetty :: Runner ................................... SUCCESS [1.705s]
[INFO] Jetty :: Http Service Provider Interface .......... SUCCESS [1.935s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 23:31.265s
[INFO] Finished at: Tue Oct 29 09:13:43 EET 2013
[INFO] Final Memory: 163M/1098M
[INFO] ------------------------------------------------------------------------

6. Build jetty-all

$ cd ~/jetty-9.1/org.eclipse.jetty.project/aggregates/jetty-all
$ mvn install