Fix for hidden overflow

[k-one-o-two]

In case of hidden overflow: IE should not include margin (added for the native scrollbar, which is hidden) in scrollTop

[k-one-o-two]

This fixes #112

[k-one-o-two]

Found a better solution: see my commit

[gromo]

I'm still thinking it's better to update browser scroll calculation function

[k-one-o-two]

But it affects the behavior of all scrolls on the page which is not good. My change really checks if this is needed