swift234

Introduce an almost completely untested implementation of constraint
generation from an expression that has not been type-checked. One can
see the constraints introduced by an expression by using

  :dump_constraints <expression>

within the REPL. We're still missing several major pieces of
constraint generation:
  - We don't yet "open up" references to polymorphic types
  - We don't print out the child constraint systems in the dump, so
  it's not at all obvious what happens within overloading (and I'm not
  convinced I like my representation anyway)
  - There are no tests whatsoever
  - Member constraints are still very, very weird



Swift SVN r2624