[JENKINS-9104] Add extension point that allows extensions to veto killing...

[FIX JENKINS-27694] Update dynamically loaded plugins' Downloadables

Typo. This list is of JobProperty, not UserProperty.

LoadStatistics: fix spacing issue in message bundle

Add @since annotation to ExtensionListListener

pretty minor, but some words were joined together when rendering the
message in the load statistics page.

When an AbstractNodeMonitorDescriptor doesn't have a result, request it via triggerUpdate()

 [JENKINS-28553] Stable workaround for adding PluginServletFilter

[FIXED JENKINS-4433] Explicitly set log4j version to 1.2.17.

Grammer fix

AbstractScmTagAction.getBuild is deprecated in favor of getRun

AbstractScmTagAction.getBuild is deprecated in favor of getRun; Jelly views should be updated accordingly.

[JENKINS-27436] Fix button link appearance

Added warning flag to shebang line, corrected string formatting, minor spelling and grammar fixes

[JENKINS-22028] update label to reflect actual behavior

Added warning flag to shebang line, corrected string formatting, minor spelling and grammar fixes to comments.

[JENKINS-2180] Always use earlier scheduling date.

[FIXED JENKINS-28926] Block while upstream/downstream building cycles never complete

- I was forgetting the call to `rebuildDependencyGraph()` which was why the test didn't work for me

- One could argue that without this change the system is functioning correctly and that previous behaviour
  was a bug. On the other hand, people have come to rely on the previous behaviour.
- The issue really centeres around state changes in the blocked tasks. Since blocking on upstream/downstream
  relies on checking the building projects and the queued (excluding blocked) tasks we need any change in
  the blocked task list to be visible immediately (i.e. update the snapshot)
- I was able to reliably reproduce this behaviour with a convoluted set of manually configured projects
  but turning this into a test case has not proved quite as easy. Manual testing confirms that the issue is
  fixed for my manual test case
- I have also added a sorting of the blocked list when probing for tasks to unblock. This should prioritise
  tasks as intended by the QueueSorter

  * documented getInstance
  * used @CheckForNull

ExtractResourceWithChangesSCM now needs to have a descriptor

Expose the type information for people's JavaScript