Change scrollbar width calculation

Antiscroll stopped working properly in Chrome v25 (it's still in dev
channel). For some reason native scrollbars are displayed under
the antiscroll generated scrollbars. The browser behaves as if ::scrollbar pseudo class
styles (setting scrollbar width/height to 0) were ignored.

I am not really sure what's causing that, but when trying to investigate
the problem I realized that scrollbarSize did not work properly in
Chrome. It was returning 0 and not the native scrollbar width.
We now calculate the size in the container with 'antiscroll-inner' class
applied. If ::scrollbar CSS is applied properly the width is 0, and we
don't have to hide native scrollbars manually. Otherwise scrollbars are
hidden by adjusting .antiscroll-inner size. That fixes Chrome v25
issue.
Merge pull request #40 from pirxpilot/chrome-25-issues

antiscroll does not work with chrome Version 25.0.1323.1 dev