fix couple of scrolling / scrollbar bugs

First commit / 53d1878 fix problem reported by at-visions:
>I use it as a pagecontrol for a textbox and have entered a ondown to a button on the scrollbar
now if the text is log so that i can scroll with the scrollbar - the ondown is working and at the end of the scrollbar the focus jumps to my button
but if the text is too short the ondown isnt working any more, focus stays on the scrollbar.

Rest of commits fix point 2. from http://forum.xbmc.org/showthread.php?tid=160627