BUG Resize infinite loops in IE8 (fixes #575)

IE8 gets a bit confused and fires resize events
when element dimensions in the DOM are changed
as a result of a resize event, causing an infinite loop.
Apart from artificially throttling the event, the only solution
I've found is to check for actual window dimension changes.
http://stackoverflow.com/questions/12366315/window-resize-event-continually-fires-in-ie7?lq=1

This implicitly fixes an issue where TreeDropdownField panel isn't
accessible in the "Insert Media" popup, because the resize event happes
to be triggered by the popup overlay, and in effect closes the drop down
panel right after opening it.

This also backports an earlier 3.1 bugfix around resize not triggering properly (8455686c).
I've tested this in 3.1 on IE8/9 and Chrome.

Relating to the jQuery UI component, there's a host of issues and discussions around this, but no solution…
http://bugs.jquery.com/ticket/4097
http://bugs.jqueryui.com/ticket/4758
http://bugs.jqueryui.com/ticket/4065
http://bugs.jqueryui.com/ticket/7514
http://bugs.jqueryui.com/ticket/8881
https://groups.google.com/forum/?fromgroups#!topic/jquery-ui/fDSvwAKL6Go
http://www.mail-archive.com/jquery-ui@googlegroups.com/msg04839.html