git-core-foo -> git-foo, except the core package

git-core-foo -> git-foo, except the core package

This patch renames the tarball "git" rather than "git-core", and changes
the names of various packages from git-core-foo to git-foo.  git-core is
still the true core package; an empty RPM package named "git" pulls in
ALL the git packages -- this makes updates work correctly, and allows
"yum install git" to do the obvious thing.

It also renames the git-(core-)tk package to gitk.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>