Implement an alias analysis pass

[pcwalton]

One of the nice things about our type system is that we have very strong alias information. We can feed this information to LLVM to help guide its optimizations.

[marijnh]

Except for object, closures, and type parameters we don't. In the alias checker, this turned out to make type-based alias analysis quite a bit harder.

[pcwalton]

That's fine. Alias analysis is hard for almost any language. We're still much better than C :)

[marijnh]

Oh, this has been done for a while now.