swift234

Big cleanup for how we handle computing types for functions and semantic
analysis for patterns.

Major changes:
1. We no longer try to compute the types of functions in the parser.
2. The type of a function always matches the type of the argument patterns.
3. Every FuncDecl now has a corresponding FuncExpr; that FuncExpr might not
   have a body, though.
4. We now use a new class "ExprHandle" so that both a pattern and a type
   can hold a reference to the same expression.

Hopefully this will be a more reasonable foundation for further changes to
how we compute the types of FuncDecls in generics and for the implementation
of type location information.



Swift SVN r2370