Merge branch 'jd/subtree'

* jd/subtree: contrib/subtree: allow adding an annotated tag contrib/subtree/Makefile: clean up rule for "clean" contrib/subtree/Makefile: clean up rules to generate documentation contrib/subtree/Makefile: s/libexecdir/gitexecdir/ contrib/subtree/Makefile: use GIT-VERSION-FILE contrib/subtree/Makefile: scrap unused $(gitdir)