swift234

Sema: Typecheck AssignExprs within the constraint system.

Set up constraints for AssignExprs within the constraint system instead of using typeCheckAssignment to set up their own isolated system. Kill the goofy hack not to consider a single-AssignExpr closure to be single-expression-body, because single-assign-expr-body closures now type-check successfully.

typeCheckAssignment still lingers because of a couple uses in typeCheckConstructorBody, but those should be easy to kill off next.

Swift SVN r5504