[JENKINS-16215] Avoiding unnecessary downloads in FilePath.installIfNecessaryFrom.

The updated version uses the locally cached timestamp, '.timestamp', to set the
'If-Modified-Since' header. 304 Not Modified responses are dealt with by
aborting the installation.
Add regression test for SurefireArchiver test mojo detection [JENKINS-8334]
[FIXED JENKINS-8334] use heuristics to detect test-mojos instead of relying on hard-coded plugin names
Additional testcase
Record start time of mojo execution in MojoInfo and use that information
to determine which test result files belong to the mojo execution
Use old method to find report files for a mojo. New method still needs some more testing.
Refactored detection of test mojos to simplify SurefireArchiver class [JENKINS-8334]
[JENKINS-16341] INSANE testing shows that a RenderOnDemandClosure binding adds about 380k, with or wothout 08efdf5.
Merge branch 'master' of github.com:jenkinsci/jenkins

at least interning some heavily redundant strings."

This reverts commit 08efdf5d3ab962cfd4c4c489266592fe1db7df8e.

Conflicts:

	changelog.html
be lenient in accepting bogus value
fixing bug that Lars found from Munich
Don't report the same plugin twice if the filtering is in use.
Linking to /threadDump.
[FIXED JENKINS-16397] Just displaying /asynchPeople constructed the expensive People object merely to decide whether or not to display the “REST API” link.
Diagnostics in case builds directory is unreadable.
A user running 1.467 reported:
java.lang.NullPointerException
    at hudson.model.RunMap.load(RunMap.java:216)
@since associated with JenkinsRule.
Merge pull request #668 from kutzi/maven-testmojo-heuristic

Use 'duck-typing' approach for detecting test mojos
Changelog and cleanup for [JENKINS-8334]
Merge pull request #660 from larshvile/master

 [FIXED JENKINS-16215] Avoiding unnecessary downloads in FilePath.installIfNecessaryFrom
[JENKINS-16215] : changelog