Add info about which pool share became stale while resubmitting.

cgminer.c

@@ -3305,7 +3305,7 @@ static void *submit_work_thread(void *userdata)
 	while (!submit_upstream_work(work, ce->curl, resubmit)) {
 		resubmit = true;
 		if (stale_work(work, true)) {
-			applog(LOG_NOTICE, "Share became stale while retrying submit, discarding");
+			applog(LOG_NOTICE, "Pool %d share became stale while retrying submit, discarding", work->pool->pool_no);
 			total_stale++;
 			pool->stale_shares++;
 			total_diff_stale += work->work_difficulty;