merge-recursive: fix memleaks

These string_list instances were allocated by get_renames() and
get_unmerged for the sole use of this caller, and the function is
responsible for freeing them, not just their contents.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-recursive.c

@@ -1858,6 +1858,9 @@ int merge_trees(struct merge_options *o,
 		string_list_clear(re_head, 0);
 		string_list_clear(entries, 1);
 
+		free(re_merge);
+		free(re_head);
+		free(entries);
 	}
 	else
 		clean = 1;