Add convenient method for checking if object is MatrixProject

This is useful for jelly pages where instanceof operator doesn't work.
the trunk is toward 1.524-SNAPSHOT
[FIXED JENKINS-18654] exlude disabled plugins from transitive dependency list
[JENKINS-18654] testcase as suggested by kutzi
[JENKINS-18654] document unit test
[FIXED JENKINS-18660] Added dedicated denormalized counter function
Delete “No” button when renaming; does not work reliably anyway.
Going back in browser history can reset configuration form to the *previous* state,
not what was just saved! (In the case of lazily inserted form elements.)
Thus clicking Save from that page would actually revert your recent changes.
For now, just omitting the button; could make it go back to index or configuration pages,
but there are already links for this.
Add unittests for Util.loadProperties
added translation for SecurityIsOffMonitor (de)
[JENKINS-17728] Fixing another possible cause of an NPE.
Unlike the bug I originally reproduced, in which the parent had some builds
but the context in which the new build was scheduled omits a parent,
this seems to be due to a case in which there is no build record at all for the parent.
No idea how that could happen (getLastBuild should return even a running, failed, or aborted build),
but @treydock reports a stack trace in 1.509.2 which implies this.
So fixing null safety; will not prevent an exception but will report it more gracefully.
[FIXED JENKINS-18671] Clock Difference broken on Manage Nodes page

System.nanos() returns a monotonically increasing value that is not related
to wallclock time. Use System.currentTimeMillis() instead.
Use System.currentTimeMillis() instead of System.nanoTime() to protect
against incorrect values if times are ever compared between different JVM nodes
Add basic ClockMonitorDescriptor test
[FIXED JENKINS-18441] NPE in MavenFingerprinter.getArtifactRepositoryMaven21.
Merge pull request #845 from oldelvet/jenkins-18671

[FIXED JENKINS-18671] Clock Difference broken on Manage Nodes page
Use JenkinsRule instead of deprecated HudsonTestCase
typo
Merge pull request #834 from vjuranek/instanceofMatrix

Add convenience method for checking if object is MatrixProject
added @since
suppress some pointless warnings