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
Host name must not be null (cloud impl should have handled such errors earlier).
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]
Merge branch 'master' of github.com:jenkinsci/jenkins
fixed NPE
bumped up MINA to a newer version
Removing I think obsolete ref to maven.jenkins-ci.org snapshot repo.
Test failure on Mac: make sure we load resources in a platform independent way.
target="_blank" for http://wiki.jenkins-ci.org/display/JENKINS/Pinned+Plugins link.
Merge branch 'master' of github.com:jenkinsci/jenkins
[FIXED JENKINS-9679] integrated remoting 2.21 that contains the fix.
Javadoc was quite confusing as the build is actually a FAILURE if tearDown returns false and not ABORTED
[maven-release-plugin] prepare release jenkins-1.499
[maven-release-plugin] prepare for next development iteration