Ref bindings explicit copy in generics

Two changes:

1. Make type parameters move by default, even if they have a Copy bound. After all, they could be bound to `~T` or `~[]`. Also, this is a necessary step towards removing `copy` keyword and replacing with clone.

2. Make it illegal to move from `*T`. This is dangerous in a "moves-by-default" scenario, because it's very easy to move when working with a `*T` pointer. Also, it requires zeroing memory, which we hope to do away with someday.