swift234

[Constraint solver] Use the new constraint solver, start deleting the old one.

The new constraint solver is very close to providing parity with the
old solver, and is significantly faster, so cut over to the new
solver. There are minor adjustments to two tests: one where we're
losing sugar (Int becomes Int64) and another where our ignorance of
overload resolution means we don't reject something silly that we
should.

Note that this only affects the *solver* component of the
constraint-based type checker; we haven't completely obsoleted the old
type checker yet.



Swift SVN r5281