Size issues in IE

This a fix suggestion for window.js line 788 to 796.

It takes the Max height for either the document or browser window and sets that as the overlay height so it always covers all the content.

@@@javascript

//IE only
positionOverlay: function(){
    var h = Math.max( document.documentElement.clientHeight, document.body.clientHeight ) + 'px';
    var w = Math.max( document.documentElement.clientWidth, document.body.clientWidth ) + 'px';

    Control.Overlay.container.setStyle({
        width: w,
        height: h
    });
}