swift234

Re-instate r2910, now that I've remembered why we need it:
essentially, we need to make sure we don't open up declarations that
don't actually have polymorphic function type, e.g., parameters. Along
with trivial constraint-generation support for TypeOfExprs, this lets
us type-check calls to the various polymorphic builtins, e.g.,
Builtin.destroy.


Swift SVN r2913