Warn on casts from raw pointers to integers

[rocallahan]

Leaking pointer bits to output is bad because it helps subvert ASLR and may provide other side channels for attackers. Preventing casts from raw pointers to integers would (AFAIK) prevent such leaks in safe Rust code.

[Manishearth]

(this would have to be a restriction lint. We'd also need to warn on things like using the debug impl of raw pointers. Can't be perfect without using metacollect or something, but can work pretty nicely.)