Bringing this to the parity with ParameterizedJobMixIn.doBuild()

Instead of returning JSON, it returns "201 Created" and responds with the location of the queue item, through which the caller can track how it passes through the queue and eventually gets built/cancelled.

The approach in pull request #750 that relies on
AbstractProject.getQueueItem() is inherently unreliable, because
item can be immediately built before the JSON is rendered, or it might
corresponds to other queued items if the build supports concurrent
builds, etc.

Massaging the pull request.

- Simplifying by reusing InterceptingExecutorService
- Not hiding the implementation class for better
  consistency with other ExecutorService impls in
  Jenkins.

[JENKINS-20974] RunParameter with filtering enabled should not include builds which have not completed

This lets us support plugins written in Java8

[FIXED JENKINS-22681] Fix of JENKINS-19418 should have used getById, not load, to avoid reloading the last build gratuitously.

masters

likewise, avoid usage of "machine" because a physical machine could host 
several nodes.

This will make the load statistics graphs fit the window width.

As per discussion under PR #1194, it should go into separate plugin.

Daemon.getCurrentExecutable() use /proc/PID/exe to retrieve the used JRE. This link is broken when the target changes (ie after a JRE system update) because the kernel appends ' (deleted)' to the symlink. This patch uses the first argument of the command line (in /proc/PID/cmdline) instead.

[JENKINS-22631] The wrong (newer) build was sometimes being marked for fixing, depending on arbitrary directory listing order.

[FIXED JENKINS-22631] Do not just warn about multiple builds with the same number; note this in the official problem list, and offer to fix it.

[FIXED JENKINS-21622] Release workspace leases (and avoid @2) even if post-build actions throw LinkageError.

Taking advantage of https://github.com/stapler/stapler-adjunct-codemirror/issues/1 for new CodeMirror.

[FIXED JENKINS-22607] Avoid loading recent builds when deletion of builds older than some date has been requested.