Test result page keeps identifying tests as age 1

If a test has not been viewed, the age will keep being 1.
This is because getFailedSince()/failedSince is lazy loaded.
Without having viewed the CaseResult that method is never
called and the prev.failedSince returns '0' which may or may
not be accurate.
http://jenkins.361315.n4.nabble.com/Problem-with-Age-column-on-Test-Results-tab-td3172208.html
[JENKINS-20739] Filter descriptors before adding them to hetero-list.

This allows implementations of DescriptorVisibilityFilter to hide items
with descriptors from users to prevent them from being added via the UI.

This is already implemented in /lib/hudson/newFromList/form.jelly, but
nowhere else.
Added logging when filtering descriptors.
Abstract username case sensitivity into an extension point
[JENKINS-22247] Provide an extension point to define user id case sensitivity contract

* Fix up bad merge
Use a dedicated descriptor
Updating the pull request in light of comments

- Removed the Legacy strategy completely
- Moved the strategy to an aspect of the security realm
- Separated the strategy for Users from Groups because... well it might be necessary for some
- Moved IdStrategy from inner class of User into top level class
[FIXED JENKINS-22395] Attempt to double-delete a Run probably caused by getNextBuild sometimes returning a build which was already deleted.
[FIXED JENKINS-20662] Establish relation to new build immediately.
[FIXED JENKINS-22672] Make /threadDump easier to use.
[JENKINS-20662] Add test.
[FIXED JENKINS-22688] Made graph font explicit and configurable
[FIXED JENKINS-22689] Show load statistics for master node
Remove repo file from RPM. https://issues.jenkins-ci.org/browse/JENKINS-22690
[FIXED JENKINS-22698] Add indicator that build queue is filtered.
[FIXED JENKINS-22699] Add option to archive only if successful
Debian postinst: check for present user/group before adding them

In git commit 7216aab0d the check for present user was removed
and therefore upgrading the Debian package on existing Jenkins
installations fails. Also the newly added code for adding a
configurable Jenkins group is missing a check for a possibly
already present Jenkins group.

Closes: JENKINS-22710
Updated w.r.t. pull request review comments
Fix test
[FIXED JENKINS-22720] Only call getAllItems in recursive ListView