Give scrollbar pseudo-classes their own blocks

A bug in Chrome 25 on Lion requires each selector to have their own blocks. E.g. the following:

.antiscroll-inner::-webkit-scrollbar, .antiscroll-inner::scrollbar {...}

causes the width and height rules to be ignored by the browser resulting in both native and antiscroll scrollbars appearing at the same time.
Calculate needXScroll with scrollbarSize
Merge pull request #51 from kapouer/patch-1

Calculate needXScroll with scrollbarSize
Merge pull request #47 from davemckenna01/chrome-25-lion-issues

Give scrollbar pseudo-classes their own blocks, fixes issue #46