normalizing parameter environments uses an empty free-region-map

[nikomatsakis]

The following program gets a (spurious) region error (E0495):

trait Project<'a, 'b> {
    type Item;
}

impl<'a, 'b> Project<'a, 'b> for ()
where 'a: 'b
{
    type Item = ();
}

fn foo<'a: 'b, 'b>()
where <() as Project<'a, 'b>>::Item : Eq
{
}

fn main() { }

The cause for this problem, I believe, is that during the normalize environment phase we use an empty FreeRegionMap, and thus do not let the region inferencer does not know that 'a: 'b holds.

I have a fix on a local branch.