Fix for IE7: Under certain circumstances, measurement of content height fails

[isrob]

Was tearing my hair out when container.contentHeight was always returning 0 on IE7, and therefore the scrollbar was never being drawn (as 0 is always less than the container height).

This line fixes it, within $.fn.scrollbar.contentHeight:

var height = wrapper.css({overflow:'hidden', zoom:'1'}).height();

(note the addition of the 'zoom' parameter to force hasLayout on the wrapper element.

Thanks very much for this fix! I was going to put in a quick conditional hack, but decided to look here first. Glad I did!