Bug #20175 identifies some rendering artifacts which started popping up when we start...

Bug #20175 identifies some rendering artifacts which started popping up when we started messing with the font sizes of Vector at the body level. The problem is that Vector was originally designed with a fixed font size set at the body level, but using fixed font sizes like px and pt (which browsers like IE 5 - 7 don't scaled with user's prefs) - so changing it to something relative caused other issues like the tabs not lining up right and such. This patch switches the approach to using a 100% font size on everything except for the actual text in the UI, usually set at the a or span tag level (closest to text as possible). Everything in the #bodyContent and #siteNotice is also scaled at that level, so content can use relative sizes as usual without any change in behavior. This approach avoids strange rounding errors which each browser seems to handle differently, making the tabs look right - while also giving users of older IE browser control over their font sizes. Thus, this fixes #20175.