http-push: fail when info/refs exists and is already locked

Failing instead of silently not updating remote refs makes the things
clearer for the user when trying to push on a repository while another
person do (or while a dandling locks are waiting for a 10 minutes
timeout).

When silently not updating remote refs, the user does not even know
that git has pushed the objects but leaved the refs as they were
before (e.g. a new bunch of commits on branch "master" is uploaded,
however the branch by itsel still points on the previous head commit).

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

http-push.c

@@ -2243,6 +2243,11 @@ int main(int argc, char **argv)
 		info_ref_lock = lock_remote("info/refs", LOCK_TIME);
 		if (info_ref_lock)
 			remote->can_update_info_refs = 1;
+		else {
+			fprintf(stderr, "Error: cannot lock existing info/refs\n");
+			rc = 1;
+			goto cleanup;
+		}
 	}
 	if (remote->has_info_packs)
 		fetch_indices();