better to define a corresponding descriptor type for backward compatibility and methods like display name.

Add new extension point (class hudson.matrix.MatrixConfigurationSorter) for enbling to sort configurations of matrix job.

It would be better to find out why the nextBuildNumber is at times empty.
In the mean time this will find the appropriate number and write it to the file.

getBuildingUpstream() to public so they can be accessed from plugins,
small refactoring (reuse getTransitiveDownstreamProjects() and
getTransitiveUpstreamProjects() respectively)

This lets us get rid of Xalan safely (as well as other often problematic
dependencies like nekohtml + Xerces combo), and reduce the dependency
footprint.

don't wake up so often when waiting for Jenkins to finish - it make take away to much time from the threads that are actually doing something

[JENKINS-11416] Added comment describing the motivation of the change. The real fix is in: ccdbd834