Iterators don't seem to work for polymorphic types

[msullivan]

iter iter2<@T>() -> T { }
fn main() {
    for each i: int in iter2() { }
}

fails with

rustc: Instructions.cpp:192: void llvm::CallInst::init(llvm::Value*, llvm::ArrayRef, const llvm::Twine&): Assertion `(i >= FTy->getNumParams() || FTy->getParamType(i) == Args[i]->getType()) && "Calling a function with a bad signature!"' failed.

[msullivan]

It works for methods, though...