Fix non-literal format in printf-style calls

These were found using gcc 4.3.2-1ubuntu11 with the warning:

    warning: format not a string literal and no format arguments

Incorporated suggestions from Brandon Casey <casey@nrlssc.navy.mil>.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -934,7 +934,7 @@ int delete_ref(const char *refname, const unsigned char *sha1, int delopt)
 			lock->lk->filename[i] = 0;
 			path = lock->lk->filename;
 		} else {
-			path = git_path(refname);
+			path = git_path("%s", refname);
 		}
 		err = unlink(path);
 		if (err && errno != ENOENT) {