Fix some things for new rust version

Some changes to make rust-sdl2 work with latest rust master.

It seems that libnative doesn't work with `rustpkg` yet. I had to do

```
sudo cp /usr/local/lib/rustc/x86_64-unknown-linux-gnu/lib/libnative-cf55a53a-0.9.so /usr/local/lib/
```

before it compiles.