Fulfill additional higher-kinded "outlives" predicates

Types fail to fulfill higher-kinded "outlives" predicates when the higher-kinded region is present on the left-hand side of the predicate. For example:

``` rust
fn foo<T>() where for<'a> &'a T: 'a {}

fn main() {
    foo::<i32>();
    //~^ ERROR the requirement `for<'a> &'a i32: 'a` is not satisfied [E0280]
}
```

CC @nikomatsakis.
