I'm exporting gitexecdir because git-gui wants to know where
it should install git-gui and git-citool. These belong under
gitexecdir, just like git-diff, as the git wrapper is able to
invoke these commands for the end-user.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org> Signed-off-by: Junio C Hamano <junkio@cox.net>