Display best share difficulty on exit.

cgminer.c

@@ -5691,6 +5691,7 @@ static void print_summary(void)
 
 	applog(LOG_WARNING, "Average hashrate: %.1f %shash/s", displayed_hashes, mhash_base? "Mega" : "Kilo");
 	applog(LOG_WARNING, "Solved blocks: %d", found_blocks);
+	applog(LOG_WARNING, "Best share difficulty: %s", best_share);
 	applog(LOG_WARNING, "Queued work requests: %d", total_getworks);
 	applog(LOG_WARNING, "Share submissions: %d", total_accepted + total_rejected);
 	applog(LOG_WARNING, "Accepted shares: %d", total_accepted);