grep: Fix two memory leaks

We duplicate the grep_opt structure when using grep threads, but didn't
later free either the patterns attached to this new structure or the
structure itself.

Signed-off-by: Dan McGee <dpmcgee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin-grep.c b/builtin-grep.c
index 9bd467c..0ef849c 100644
--- a/builtin-grep.c
+++ b/builtin-grep.c
@@ -205,6 +205,8 @@
 
 		work_done(w);
 	}
+	free_grep_patterns(arg);
+	free(arg);
 
 	return (void*) (intptr_t) hit;
 }