Fixes external http://code.google.com/p/android/issues/detail?id=2732....

Fixes external http://code.google.com/p/android/issues/detail?id=2732. ExpandableListView is wrongly assuming that the saved state if of the correct type. A similar bug fix was made in TextView.onRestoreInstanceState() a while ago. This fix simply ensures that the state received is of the right type.