Update the order when predicating blocks. (#1859)

When doing predicate blocks, we need to traverse every block in
structured order in order to keep track of which construct a block is
contained in.  The standard way of traversing code in structured order
is to create a list with all of the nodes in order.  However, when
predicating blocks, new blocks are created, and those blocks are missed.
This causes branches that go too far.

The solution is to update the order as new blocks are created.  Since
we are using an std::list, we do not have to worry about invalidation of
iterators when changing the list.