[JENKINS-19622] Merged #989: allow background tasks to run simultaneously, preventing task blockage.

Merge branch 'scheduled-executor-timer' of github.com:recampbell/jenkins into recampbell-scheduled-executor-timer

A few usages of Hudson.getInstance() were actually mandated for use with method signatures which cannot compatibly be changed.

Javadoc warning fixes for CLICommand, Run, and ViewOptionHandler

If TopLevelItemDescriptor.newInstance throws a RuntimeException, why are we wrapping it in an IllegalArgumentException?
Let it throw something like Failure and control the rendering.

Remove weird chars from Javadoc.

Probably a copy+paste caused these extra characters in there.

Normally this is only printed during functional tests or during in-process restart.
In neither case do we really want to see a log message (i.e. two lines of text) for each plugin in the system being stopped.