Comment resource appears to ignore pid for threaded comments

It appears that in comment_resource.inc on line 188 the creation of the empty comment object should include the pid (parent ID) value if provided by the request for the comment_form to properly process threaded comments.

$comment_empty = (object) array(
'nid' => $comment['nid'],
'cid' => NULL,
);

should be

$comment_empty = (object) array(
'nid' => $comment['nid'],
'cid' => NULL,
'pid' => $comment['pid'],
);

This appears to work in our limited testing and appears to pass the pid into the comment_form successfully for threading to occur.