The actual fix has been implemented over the last dozen or so commits

Existing implementations are retrofitted to the new extension point.

Adding extension point so that the master can install code that restarts JNLP slaves.

[FIXED JENKINS-18364] Functions.getRelativeLinkTo is called many times during rendering, so skip checking View.getItems which is expensive.

Avoid extracting war file under /tmp. When jar files and resource files disappear from under
us, all sorts of strange errors happen.

Being defensive.

[JENKINS-22397] Allow a Trigger to be a DependencyDeclarer

Merge branch 'master' of git://github.com/jenkinsci/jenkins into Trigger-DependencyDeclarer-JENKINS-22397