Add git-blame, a tool for assigning blame.

I have also been working on a blame program. The algorithm is pretty
much the one described by Junio in his blame.perl. My variant doesn't
handle renames, but it shouldn't be too hard to add that. The output
is minimal, just the line number followed by the commit SHA1.

An interesting observation is that the output from my git-blame and
your git-annotate doesn't match on all files in the git
repository. One example where several lines differ is read-cache.c. I
haven't investigated it further to find out which one is correct.

The code should be considered as a work in progress. It certainly has
a couple of rough edges. The output looks fairly sane on the few files
I have tested it on, but it wouldn't be too surprising if it gets some
cases wrong.

[jc: adding it to pu for wider comments. I did minimum
whitespace fixups but it still needs an indent run and
-Wdeclaration-after-statement fixups.]

Signed-off-by: Fredrik Kuivinen <freku045@student.liu.se>
Signed-off-by: Junio C Hamano <junkio@cox.net>