send-pack: tighten checks for remote names

"git push $URL HEAD~6" created a bogus ref HEAD~6 immediately
under $GIT_DIR of the remote repository.  While we should keep
refspecs that have arbitrary extended SHA-1 expression on the
source side working (e.g. "HEAD~6:refs/tags/yesterday"), we
should not create bogus ref on the other end.

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

refs.c

@@ -534,7 +534,7 @@ int check_ref_format(const char *ref)
 		level++;
 		if (!ch) {
 			if (level < 2)
-				return -1; /* at least of form "heads/blah" */
+				return -2; /* at least of form "heads/blah" */
 			return 0;
 		}
 	}