"Invalid cast" on some uses of bottom

[jruderman]

fn main() { log_err fail; }

gives

Assertion failed: (S->getType()->isPointerTy() && "Invalid cast"), function getPointerCast, file Constants.cpp, line 1275.

[brson]

Probably the same problem: there's a failing test case for 'log ret' in run-pass/wierd-exprs.rs