[JENKINS-20534] Avoid usage of temporary file to write symlink.

Creating a symlink is an atomic operation, and additionally
usage of tmp file + rename performs very badly on NTFS file
system because of the way the rename is tracked in the $MFT.

In case symbolic links are not supported, we still fallback to
a regular file.
the trunk is toward 1.552-SNAPSHOT
Merge branch 'avoid_symlink_rename' of https://github.com/Vlatombe/jenkins
[FIXED JENKINS-20534] Noting merge of #1057.
Warn user when plugin dependencies don't match
required minimal version
Use dedicated exceptions to track incompatible/missing plugin
to be used by other component to log/resolve configuration issue.
minor simplification
groovy null-safe operation, I miss you.
When printing AbstractBuild.BuildingRemotely message to log, also indicate any (non-self) labels of the node.
This is invaluable when diagnosing problems with a build on a cloud slave after the slave has been deprovisioned.
If the node name by itself does not indicate what type of machine it was, you would have a hard time guessing.
[FIXED JENKINS-21780] DirectoryBrowserSupport.FileComparator should cache isDirectory calls.
Revert "groovy null-safe operation, I miss you."

This reverts commit 037393c28aad8b8d7d59994328ae7d3ec1f45ee7.
Revert "minor simplification"

This reverts commit 6a31d6ebb47f310b2039dcd69085bba1583e3159.
Revert "Use dedicated exceptions to track incompatible/missing plugin"

This reverts commit b32d0e4f7414e4f144148e8e39cc308b2f9131a8.
Revert "Warn user when plugin dependencies don't match"

This reverts commit 2d40b7e7e9f5f6cd669cb0e3ba8625d05795dabe.
[FIXED JENKINS-21777] Actions contributing to Labels' index page
[FIXED JENKINS-21778] Fix sidepanel links so they don't break from Actions
Add changelog recoed for PR #1128
[FIXED JENKINS-21772] Only cache CLI credentials in ~/.hudson if it exists.
Add changelog record for PR #1127
Strengthening the reverse proxy admin monitor to detect nontransparent slash encoding (/ vs. %2F).
Apache in its default configuration botches this: http://stackoverflow.com/a/9933890/12916