git-sh-setup: do not use repo-config to test the git directory
git-sh-setup: do not use repo-config to test the git directory

Since repo-config does not fail in non-git directory, it is not
a good command to use to test the git-ness nor validate the
repository revision of $GIT_DIR.

Original patch by Robert Shearman but with minor fixes.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git