This gives more flexibility to build systems that don't run genrevision with desired destination as working dir.
For example a build system may run:
build/tools/genrevision -o build/src/shared/revision.h
* Changed genrevision to use * instead of unknown when some info can not be found
* Added the git_id tool which is used to generate changes to revision_nr.h and the commit message
Also svn_revision.h renmaed to revision.h and defines in to it also renamed. MaNGOS code updated.
Other projects using this genrevison tool need to be updated in similar way.