Comments, and some small changes:
Comments, and some small changes:

  1. Preserve order of TODO list, os that we prefer unification variables
  2. Stop early when looking for `x = y`.

So if we have 'a = b = c` now we'll get:

a = b
b = c

Before we would get:
a = b
a = c

ntc2/cryptol,GaloisInc/cryptol,GaloisInc/cryptol,GaloisInc/cryptol