fix #637 HTML radio button not reacting in IE 7

Radio button needs a name to get selected by a click in IE7.
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.
bug spotted in IE 7:

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.