(cherry picked from commit 2e5a7bf4)

CauseOfBlockage not displayed when build blocked by QueueTaskDispatcher.canRun()

[JENKINS-10880] output the job when polling fails

if the root URL isn't configured, clients won't be able to find this, so might as well not advertise at all.

Fixed changelog

[FIXED JENKINS-13389] Moved "View as plain text" link on console output ...

use prefix to static resources not to pick up stale cache.

[FIXED JENKINS-13454] Optimize the plugin manager

[FIXED JENKINS-13387] Converted "Delete this build" buttons into links in the sidepanel

update to guava 12.0-rc1

It should return null for those cases instead.