[JENKINS-17526] Relocating Jetty/Java tmpdir for Mac OS X.

Warn in the UI about short cycles in the day of month field for a crontab, which can have surprising behaviors near the end of a month.

Replaced “New Job” with “New Item” since various plugins (such as cloudbees-folder) add TopLevelItemDescriptor’s which do not produce Job’s.
(Might be feasible to automatically use “Job” or “Item” according to the most specific common supertype of all registered descriptors?)

When downloading a zip file with all of the artifacts, file descriptors
would be opened and never closed. This resulted in many leaked file
descriptors which would only be cleaned up the next time the garbage
collector was run.

For directories with a large number of files, the zip file would be
corrupted because an exception was thrown during the process of creating
the zip file when the process ran out of file descriptors. Jenkins was
then left in a very brittle state as random threads wouldn't be able to
open files or sockets anymore until the garbage collector was run.

[FIXED JENKINS-21371] Enhance SecurityRealm API to support queries of the group membership

Add tests

Method getComputers() does not return computers for label expressions.

Use -Djava.awt.headless=true on Debian service

I installed the Jenkins Debian package, and later installed an XServer (XVFB).  The graphs of test results etc. were replaced by an image suggesting that I add this flag to the JVM commandline.  I don't see any reason why this shouldn't always be present on Debian systems.

purged some messages that are obsolete since
06514d25
localized redirect message

[FIXED JENKINS-18694] Generalizing fix of JENKINS-18678 to include also rename of parent folders, taking advantage of JENKINS-18028 API.

[JENKINS-18224] Relaxing type parameter restriction on TransientActionFactory since useful mixin interfaces like Item do not extend Actionable.

[JENKINS-18224] TransientActionFactory

[FIX JENKINS-21303] There is a NPE here that can and does happen for real when an aggresive slave retention strategy interacts with post build triggers that want to do token macro expansion