merge-recursive: Make BUG message more legible by adding a newline

Hopefully no one ever hits this error except when making large changes to
merge-recursive.c and debugging...

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-recursive.c

@@ -230,7 +230,7 @@ struct tree *write_tree_from_memory(struct merge_options *o)
 		for (i = 0; i < active_nr; i++) {
 			struct cache_entry *ce = active_cache[i];
 			if (ce_stage(ce))
-				fprintf(stderr, "BUG: %d %.*s", ce_stage(ce),
+				fprintf(stderr, "BUG: %d %.*s\n", ce_stage(ce),
 					(int)ce_namelen(ce), ce->name);
 		}
 		die("Bug in merge-recursive.c");