JENKINS-21160: update pom.xml to warn about mismatched args4j

in some circumstances, you may use some older args4j (coming from remoting) when the jenkins about page shows a different version.
the trunk is toward 1.587-SNAPSHOT
Null safety.
Observed in a test against 1.480:
… hudson.model.Executor run
SEVERE: Unexpected executor death
java.lang.NullPointerException
	at hudson.model.Computer.getNode(Computer.java:473)
	at hudson.slaves.SlaveComputer.getNode(SlaveComputer.java:177)
	at hudson.slaves.SlaveComputer.getRetentionStrategy(SlaveComputer.java:609)
	at hudson.slaves.SlaveComputer.taskCompleted(SlaveComputer.java:285)
	at hudson.model.queue.WorkUnitContext.synchronizeEnd(WorkUnitContext.java:140)
	at hudson.model.Executor.run(Executor.java:253)
[FIXED JENKINS-25280] Failed tests do not get displayed properly in the overview

there is no such mothod getFullDisplayName in a TestObject - only getDisplayName

Change-Id: Idd454be00a22ee3c93f661a3ee3ae322a25c271d
[FIXED JENKINS-15252] Explain problems with CSRF protection
Change the javadoc of UpstreamCause to be more accurate (the upstream build need not be complete)
Merge pull request #1441 from mattmoor/upstream-javadoc

Change the javadoc of UpstreamCause to be more accurate...
junit 1.2-beta-3
[FIXED JENKINS-24527] Update jna-posix to 1.0.3-jenkins-1 which uses JNA 4.1
[JENKINS-24527] Noting merge of #1442.
Integrated the newest Stapler version

In particular, this includes pull request #39 from Matt that handles
'$class'
Forgotten @since.
Merge REMERGE_HEAD into HEAD
[FIXED JENKINS-25314]

The original fix was made in 0c3d67097a3394fee7f0eb895c4350ea96887a02.
In this fix, I'm also moving the code that creates LeftItem.

It makes no sense that there's Item.cancel(Queue) and Queue.cancel(Item)
and they do different things!
Merge commit '9b36e2ae8dbbd2a7ab0d9d4bc9e24e305e33ecbc'
[maven-release-plugin] prepare for next development iteration
updated changelog for release
updated changelog as a part of the release
merged back the RC branch
creating an RC branch