Fix glob import stack overflows

The rust stdlib suddenly got a bunch of additional glob imports when enums got namespaced.
Unfortunately racer follows each glob recursively which makes it stack-overflow.

Instead for now racer is just traversing one glob at a time. This means it cannot find matches that
require nested globs. Hopefully this doesnt happen in the wild too often.
e.g.

pub use mymod::*;
pub use MyEnum::*
mod mymod {
    MyEnum { MyVariant };
}

MyVariant  // <--- racer cannot find this