swift234

Add command line options to turn on the two LangOptions options for
the constraint-based type checker:

  -constraint-checker turns on constraint-based type checking for the
   current swift module (but not imported modules; we're not ready for that)
  
  -debug-constraints turns on detailed debugging information for the
   constraint-based type checker

Use these flags to de-REPL-ify the tests for the constraint-based type
checker. The REPL is still quite useful for experimenting with the
type checker, but shouldn't be our normal means of testing it.



Swift SVN r2840