[FIXED JENKINS-18417]

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

(cherry picked from commit 216f5c6a45ed4f5e592817ed6192d5b5fc1dee24)

Conflicts:
	changelog.html
[FIXED JENKINS-19515] Try to avoid truncation of fingerprint storage files.
1. Use AtomicFileWriter on the hypothesis that an exception during save() caused truncation.
2. Improve logging from the cleanup thread since that may be related to the root cause.
3. Regardless of the cause, recover more gracefully by deleting any truncated file rather than throwing the error up.
(cherry picked from commit 7790dbcabfcfe3aeb8db54cf13673036e0548d34)

Conflicts:
	changelog.html
@Bug
(cherry picked from commit 2c23e643fac3efef98eec03b83adf735f07a2d62)
[FIXED JENKINS-15578]

The slave launch thread is another background thread, and it should run
like a super-user

(cherry picked from commit 4a71b011613f8e8c5a31b6b4dee66de43aa4f4dc)

Conflicts:
	changelog.html
Level.getLocalizedName should be preferred to Level.toString().toLowerCase().
Consider the poor Turk who is prompted to log at fıner!
(cherry picked from commit 2527778d3b4b91c6de57b39f05d1582ca10dd4f3)
2527778d amended to display Level.localizedName but track Level.name in the form submission.
(cherry picked from commit dd28e970499b4785116a7fe98530534f0dc04590)
JUnit 4.
(cherry picked from commit 6ea8c4943d0a25b6049e354836d6e87005964703)
[FIXED JENKINS-18274] LogRecorder.getSlaveLogRecords
(cherry picked from commit d10fbc5eace959d3a5928d40b1c1f8975b3be1d0)
[JENKINS-18274] ComputerListener methods should be called as ACL.SYSTEM.
https://ci.jenkins-ci.org/job/jenkins_main_trunk/2588/testReport/junit/hudson.bugs/JnlpAccessWithSecuredHudsonTest/testServiceUsingDirectSecret/
(cherry picked from commit ca5304307607a9bddfb472cf6dc014ed5c0f8f83)