git-gui is using "git-read-tree -u" when cloning which doesn't
invoke the post-checkout hook as a plain git-clone would.
So git-gui must call the hook itself.
Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de> Signed-off-by: Shawn O. Pearce <spearce@spearce.org>