Started producing 1.6 class files

The plan of the record is that we start producing 1.6 class files and
see if people start complaining. If we hear from users, we'll re-visit
our decision, and if we don't, then we'll start using 1.6 features
everywhere in the code.

changelog.html

@@ -75,6 +75,10 @@ Upcoming changes</a>
   <li class=rfe>
     Executors running the builds can be now a subject of access control.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-18285">issue 18285</a>)
+  <li class='major rfe'>
+    Core started relying on Java 1.6 as per the agreement in the dev list.
+    If you have a serious objection against it, please let us know
+    before we really start relying on 1.6 features.
 </ul>
 </div><!--=TRUNK-END=-->
 

pom.xml

@@ -598,8 +598,8 @@ THE SOFTWARE.
       <plugin>
         <artifactId>maven-compiler-plugin</artifactId>
         <configuration><!-- we specify this in the parent POM, so this is redundant, but otherwise IntelliJ is unhappy -->
-          <source>1.5</source>
-          <target>1.5</target>
+          <source>1.6</source>
+          <target>1.6</target>
           <!-- default reuseCreated is more performant 
           feel free to uncomment if you have any issues on your platform
           <compilerReuseStrategy>alwaysNew</compilerReuseStrategy>