Make "parse_object()" also fill in commit message buffer data.

And teach fsck to free it to save memory.

commit.h

@@ -14,7 +14,7 @@ struct commit {
 	unsigned long date;
 	struct commit_list *parents;
 	struct tree *tree;
-	const char *buffer;
+	char *buffer;
 };
 
 extern const char *commit_type;

fsck-cache.c

@@ -203,6 +203,8 @@ static int fsck_tree(struct tree *item)
 
 static int fsck_commit(struct commit *commit)
 {
+	free(commit->buffer);
+	commit->buffer = NULL;
 	if (!commit->tree)
 		return -1;
 	if (!commit->parents && show_root)

object.c

@@ -129,6 +129,10 @@ struct object *parse_object(unsigned char *sha1)
 		} else if (!strcmp(type, "commit")) {
 			struct commit *commit = lookup_commit(sha1);
 			parse_commit_buffer(commit, buffer, size);
+			if (!commit->buffer) {
+				commit->buffer = buffer;
+				buffer = NULL;
+			}
 			obj = &commit->object;
 		} else if (!strcmp(type, "tag")) {
 			struct tag *tag = lookup_tag(sha1);