Fixed some bug in xp sp3 ie7 & ie6 and add an example

1. fixed mouse scroll over blank area bug.
2. fixed contentHeight and contentWidth retrieve.
3. add an examples based on text content.
4. fixed the unsupported ':hover' pseudo-class  in ie6.
5. fixed the position of scrollbar when scroll in ie6.
6. fixed the size of scrollbar in ie6