Binary operations are not type checked

[brson]

This fails in trans:

fn main() {
  auto x = true;
  auto y = 1;
  auto z = x + y;
}

[msullivan]

We still don't make sure that the type is a sensible one to perform the binary operation on, though:

fn main() {
    auto x = tup(true) + tup(false);
}

still passes the typechecker (and fails from an llvm assert).