Ben Gamari authored Jan 05, 2016 and Ben Gamari committed Jan 05, 2016

The interfaces to {save,load}ThreadState were quite messy due to the
need to pass in local registers (produced with draws from a unique
supply) since they were used from both FCode and UniqSM.

This, however, is entirely unnecessary as we already have an
abstraction to capture this effect: MonadUnique. Use it.

This is part of an effort to properly represent stack unwinding
information
for foreign calls.

Test Plan: validate

Reviewers: austin, simonmar

Reviewed By: simonmar

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1733