Integrated the fix into Jenkins

... with a test case. The fix is in Stapler.

System.nanos() returns a monotonically increasing value that is not related
to wallclock time. Use System.currentTimeMillis() instead.

Unlike the bug I originally reproduced, in which the parent had some builds
but the context in which the new build was scheduled omits a parent,
this seems to be due to a case in which there is no build record at all for the parent.
No idea how that could happen (getLastBuild should return even a running, failed, or aborted build),
but @treydock reports a stack trace in 1.509.2 which implies this.
So fixing null safety; will not prevent an exception but will report it more gracefully.

The earlier fix by @ssogabe broke the test. This fix corrects the
problem properly.

The reason this error happens with some plugins is that if there's an
input field whose name is "on", then even after prototype.js extends
an element object, "form.on" will refer to the input element, not the
prototype.js function to add an event handler.

Use DescribableList to handle the copy-on-write semantics correctly. The vector class just doesn't cut it, and we've been setting a new value to this field, which will violates all sorts of the concurrent programming practice.

This change has the nice side effect of removing {{class="vector"}} from the persisted XML. A test is added to make sure we can still read back such an XML.

Revisiting the fix. Avoid parsing the entire text by only looking at the tail portion.

Node monitoring should run in parallel to reduce the total round-trip
time in large instances.

Integrated the fix toward 1.521.

Based on further conversation with the Artifactory plugin developers, revisiting this extension point.

This is a breaking change, but this extension point was added very recently, and it's based on the input from Artifactory plugin, so there's not much point in keeping one that doesn't serve the intended use case.

"201 Created" response doesn't work well with a browser as the user agent.

The exception handler ended up adding almost all the headers again,
resulting in a lot of duplicate headers.

Most critically, stapler was adding "Content-Encoding" header twice,
breaking browsers.

Integrated the new version of remoting

Fire the "jenkins:apply" event from the apply button and listen to that to write back edits to <TEXTAREA>

Exposed the UI that sets the assigned label of matrix projects.
This deprecates the "Matrix tie parent" plugin.

Reimplemented a proper topological sort and generates a total order
comparison function.

FingerprintCleanupThread can now partially clean up a fingerprint record
by removing portions of it that's not referencing existing stuff.

[JENKINS-17713] [FIXED JENKINS-14362] These fixes were (mistakenly?) recorded for 1.518 rather than for trunk.