Prototype

Before the recent patches

http://prototype.lighthouseapp.com/projects/8886/tickets/162-git-element-cumulativeoffset-and-getdimensions-not-working-as-expected

I had initially removed the this.deltaX and this.deltaY compensations because they were
not needed when things were being calculated wrongly (before Sundays patches).
Now that those methods are working this needs to be reverted
(add back the - this.deltaX and this.deltaY).

This will fix Firefox, Opera 9.25. 9.5, Safari 3.

IE will still fail on them but thats a deeper issue (its getting the offsetParent() of 
document.body and adding its offset where it would normally be getting HTML element 
(inconsistent with other browsers and add its offset values which are 0).
It might have something to do with it being an absolutly positioned element. 
(nicks functional tests don't appear off and the dom_test unit test pass).

(deprecated.js)

withinIncludingScrolloffsets: 
function(element, x, y) {
  var offsetcache = Element.cumulativeScrollOffset(element),
  dimensions = Element.getDimensions(element);
  
  this.xcomp = x + offsetcache[0];
  this.ycomp = y + offsetcache[1];

should be:

withinIncludingScrolloffsets: function(element, x, y) {
  var offsetcache = Element.cumulativeScrollOffset(element),
  dimensions = Element.getDimensions(element);
  
  this.xcomp = x + offsetcache[0] - this.deltaX;
  this.ycomp = y + offsetcache[1] - this.deltaY;