fixed [JENKINS-15408]: Rotation of slave launch logs on Windows

Merge branch 'master' of https://github.com/jenkinsci/jenkins into ReopenableRotatingFileOutputStream-windows

[JENKINS-13202] 646154f1 refinement: resolveSymlink is documented to return null, not throw an exception, when called on a regular file.

The bug was actually already fixed and moreover this could cause that fireCompleted won't be called in case that cleanUp throws an exception, see commentes under https://github.com/jenkinsci/jenkins/commit/51f715162eba4dd1c4e081ec15c7ceb12e813ca5

Prevent to exception which causes that build will not be saved.

Conflicts:
	changelog.html

[JENKINS-15367] Fix Maven downstream resolution when declared as a specific version.

Document when EnvVars.get() function was added.

Set source/target level to 1.6 within the m2e profile.

Otherwise, eclipse gets unhappy with the @Override annotations.

inverse maven-plugin -> config-file-provider dependency