dereferencing a single-variant enum allowed in typeck, hits LLVM assert in trans

``` rust
fn main() {
    enum Foo { Bar(int) }
    let _x = *Bar(2);
}
```

```
rustc: /build/rust-git/src/rust/src/llvm/lib/IR/Instructions.cpp:1084: void llvm::StoreInst::AssertOK(): Assertion `getOperand(0)->getType() == cast<PointerType>(getOperand(1)->getType())->getElementType() && "Ptr must be a pointer to Val type!"' failed.
```
