This is a simplification of the dialog overlay/modal code. This PR is just to start a discussion and get feedback.
This drops support for IE 6 because of fixed positioning.
The overlay now uses fixed positioning and is sized to 100%x100%. This removes the need to constantly adjust the size of the overlay and let's us stop hacking around dimension issues in various browsers. This needs to be checked in all browsers to make sure this doesn't cause scrollbars and works as expected.
We now cancel events based on whether the element is inside a dialog, not what the z-index is. This almost certainly will break existing functionality, such as autocomplete and datepickers inside dialogs. We need to find a better solution. If an event occurs on an invalid element, we now shift focus back to the dialog. We need to figure out a way to know which dialog to focus when this happens.
The overlay no longer handles pressing escape because it should never have focus now (focus should shift back to the dialog).
There's probably other stuff I haven't thought of yet...
Dialog: Simplify overlay code.
Landed in 86a05cb (see dialog branch for now)