This is the latest Java 7 compatible jgit release.
Properly support GitHub tags marked as "Pre-release".
With the previous venerable jgit version 1.1.0, a YaCy repository clone
having such a tag made GitRevTask and GitRevMavenTask crash.
do not handle the revision in build.properties anymore
(9000 as fallback)
build-date from git-HEAD (instead when build is fired)
(orginal build-date as fallback)