Convert `T::Foo` resolution to use where clauses, not bounds

[nikomatsakis]

Currently referencing an associated type like T::Foo searches the bounds on T rather than the full set of where clauses. This is no good.

[nikomatsakis]

Nominating and placing on 1.0 alpha milestone. Ultimately PROBABLY a nice to have, but it's really surprising that this doesn't work.

[jroesch]

cc me

[erickt]

Until this is implemented, you can also use a qualified type path <T as Trait>::Item:

trait Trait {
    type Item;
}

struct Foo;

impl Foo {
    fn foo1<T: Trait>(_x: T::Item) {}

    fn foo2<T>(_x: <T as Trait>::Item) where T: Trait {}
}

struct Bar;

impl Trait for Bar {
    type Item = i32;
}

fn main() {
    Foo::foo1::<Bar>(5i32);
    Foo::foo2::<Bar>(5i32);
}