Adjust my prior change to better utilize structured form submission to accomodate a few plugins that are improperly submitting data through this processing logic

fromExternalizableId should just return null, not throw IAE, if the job has since been renamed/move/deleted.
(It could already return null if the run has since been deleted; #1264 failed to mark this properly.)
Reserving IAE for inputs that getExternalizableId could not actually have produced,
and making sure to also throw this in case of non-numeric text after the hash.
Adding Javadoc for both methods.

- Yet more interrupting bad patterns, especially where we expect the node monitor to take up to 30 seconds to complete if an async variety

Prevent a storm of node monitor updates when there is a storm of nodes coming on line within 1 second

- The old code would result in multiple triggered updates, with corresponding interrupts of in-progress updates
  when faced with lots of slaves coming on line within 1 second of each other.

- New code will ensure that one and only one of the scheduled tasks (i.e. the last one) will trigger the updates.

Refactor NodeProvisioner to allow for extension of strategies

... as it grants access to the JVM internals of the master in the same
Groovy scripts do.

JENKINS-21160: update pom.xml to warn about mismatched args4j

[FIXED JENKINS-15252] Explain problems with CSRF protection

Conflicts:
	pom.xml

Conflicts:
	pom.xml

The original fix was made in 0c3d6709.
In this fix, I'm also moving the code that creates LeftItem.

It makes no sense that there's Item.cancel(Queue) and Queue.cancel(Item)
and they do different things!

(cherry picked from commit b19f4650)

Conflicts:
	changelog.html
	war/pom.xml