fix #638 testcase for radiobutton issue in IE7

radio button needs a name to get selected by a click. As there is no need for a name in this widget,
the workaround is to call the onbind method on every radio button bound to the model.
fix #642 Some wrong scrollbars were displayed in the splitter panels.

In these cases, this prevented from scrolling the content panel.
Some miscalculations of the width and height have also been fixed.
The splitter border  width is now accessible from the skinning system (by the new borderWidth property).