Instead of local-expanding the entire top-level forms at
once, wrap expressions in a top-level begin in trampolining
macro forms. This allows the typechecker to trampoline back
to the evaluator, which is necessary to declare/register
declarations made in a top-level begin.
The point of this change is to eliminate top-level hacks
and faciliate various macros that need to communicate using
multiple top-level forms.
