swift234

Sema: Check func operator arity syntactically.

This gives us a couple things:

- It lets name binding match up operator funcs to operator decls reliably without depending on unary operators being properly attributed;
- It allows unary operators on tuples to be distinguished from binary operators; the former should always be declared 'func +(_:(x:A,y:B))', and the latter as 'func +(x:A,y:B)'.

Swift SVN r4636