swift234

implement isa/dyncast and dumping support for exprs.
We can now parse and print this:
var x3 = 4+5*4+12/97;

into:
(vardecl 'x3'
 (binary_expr
  (binary_expr
   (integer_literal 4)
   (binary_expr
    (integer_literal 5)
    (integer_literal 4)))
  (binary_expr
   (integer_literal 12)
   (integer_literal 97))))




Swift SVN r46