@cvrebert do you think that the static-nav cases should handled elsewhere?

The change from inspecting `window.innerHeight` to checking `window.innerWidth` to denote the presence of scrollbars should fix the solution that's already out there while leaving the `navbar-fixed-[whatever]` alone (i.e., leaving them shifting right).

Would this pull request be better to just address the issue with IE10/11?

I'm really eager to see some fix roll so that I can update my own codebase.