swift234

Fix places in the constraint solver where it would give up once a single 
constraint failed, leaving a bunch of other solvable constraints laying 
around in the system as inactive.

This is a problem for diagnostics emission, because it turns around and
reaches into the constraint system for some inactive constraint, assuming
that anything left could not be solved.  The constraint system attempted to
solve this by taking the first failure and putting it into the failedConstraint
with the intention of driving diagnostics, but just because it happened to fail
first in constraint-solver-worklist-order doesn't mean it is the most pertinent
one to diagnose.



Swift SVN r30787