Draggable: Avoid using scrollWidth and scrollHeight for containment calculations

scrollWidth/scrollHeight should not be used to calculate containment since they produce inconsistent values between Webkit and all other browsers. It seems more straightforward to just rely on the offsetWidth/offsetHeight of the element.

Webkit browsers will calculate the scrollWidth and scrollHeight differently then all other browser in the following scenario:

Containment element for the Draggable module has absolutely positioned elements that overflow the container. Unless the overflow is set to hidden jQuery will use the scrollWidth and scrollHeight. In Webkit scrollWidth/scrollHeight includes the absolutely positioned elements while all other browsers do not.

co.left+(over ? Math.max(ce.scrollWidth,ce.offsetWidth) : ce.offsetWidth) - (parseInt($(ce).css("borderLeftWidth"),10) || 0) - (parseInt($(ce).css("paddingRight"),10) || 0) - this.helperProportions.width - this.margins.left,
co.top+(over ? Math.max(ce.scrollHeight,ce.offsetHeight) : ce.offsetHeight) - (parseInt($(ce).css("borderTopWidth"),10) || 0) - (parseInt($(ce).css("paddingBottom"),10) || 0) - this.helperProportions.height - this.margins.top