Display classLoadingPrefetchCacheCount.
Merge branch 'prefetch-JENKINS-15120'

Conflicts:
	pom.xml
fixed @since
Make assertGC more useful by showing root references in case of failure.
Queue.clearLeftItems to fix AbstractProjectTest.testGetBuildAfterGC test failure after 84a2593.
stephenc asks to use TODO rather than XXX
maven-surefire-plugin 2.15 for SUREFIRE-968 fix: show which test finished even under concurrency.
[JENKINS-16952] contextDestroyed needs to be changed to match.
ALL is a more sensible default value than SEVERE (which would be logged anyway).
Level.getLocalizedName should be preferred to Level.toString().toLowerCase().
Consider the poor Turk who is prompted to log at fıner!
[JENKINS-16952] [JENKINS-18274] Slave computers should record all log messages at INFO+, not just those in the hudson.* namespace.
2527778d amended to display Level.localizedName but track Level.name in the form submission.
JUnit 4.
[FIXED JENKINS-18274] LogRecorder.getSlaveLogRecords
Better diagnosis when resolvePluginFile would be about to return null.
If urlChildPrefix is ".", do not prefix shortUrl with "./".
[JENKINS-18274] ComputerListener methods should be called as ACL.SYSTEM.
https://ci.jenkins-ci.org/job/jenkins_main_trunk/2588/testReport/junit/hudson.bugs/JnlpAccessWithSecuredHudsonTest/testServiceUsingDirectSecret/
[maven-release-plugin] prepare release jenkins-1.518
[maven-release-plugin] prepare for next development iteration
updated changelog for release