Fix cfor inlining bug.

This ended up being a bit subtle. Basically, the transform() method
doesn't correctly handle the following kinds of trees:

TypeTree().setOriginal($tree)

Basically, in this case transform() method doesn't recursive into the
$tree, but the $tree is actually where the important code is. We fix
this by matching TypeTree explicitly and calling transform($tree) when
$tree is not null.