Make sure that change log annotation cannot result into exception

Although javadoc for ChangeLogAnnotator#annotate() states that any exception should be caught in this method and it should return normally, some implementation don't respect it or e.g. in case of missing some dependecy (resulting into NoClassDefFoundError) plugin itself can hardly ensure that no exption is thrown. We should ensure it on the core level.
[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-16342] Improving responsiveness of asynchPeople when Gravatar plugin is in use.
This change does not necessarily improve total performance, since the avatar is still computed.
But (1) the computation is correctly done in the work thread, not in the HTTP response thread;
(2) the computation is done just once for a given User, which could reduce load when many AJAX checks are done.
Merge remote-tracking branch 'jenkins/master'
Merge pull request #650 from vjuranek/changelog_except

Make sure that change log annotation cannot result into exception
[FIXED JENKINS-16278] Fixed RememberMe cookie signature generation (bugfix on SECURITY-49)

New cookie signature generation was not implemented in creation of RememberMe cookie, but only in its verification.
Fixed by new override TokenBasedRememberMeServices2.loginSuccess
[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
Fix license text.
Add missed closing parenthesis.
Update the url of Hudson.USER_CONTENT_README.
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.