[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.
[FIXED JENKINS-21673] Sort authorities on user index page.
Merge branch 'JENKINS-21673' of https://github.com/daniel-beck/jenkins
[JENKINS-21673] Noting merge of #1120.
The original fix was lost when Winstone became 2.0
Improvements to API documentation.

* Added requirement to send header when POSTing config.xml.
* Don't tell anyone with Overall/Read where JENKINS_HOME is located
* Add an alternative to viewing config.xml files on the server for non-admins
Merge pull request #1122 from daniel-beck/api-doc

Improvements to API documentation.
[maven-release-plugin] prepare release jenkins-1.550
[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
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.