New method for detecting hidden outputs

This changes the method for detection hidden outputs, from checking for 0-width and 0-height, to checking for the CSS style display:none.

This new method seems to be plenty fast for simple apps like 06_tabsets, but it should be tested on more complicated apps. This information from the jQuery docs shows a big increase in speed when they changed their `:visible` selector from using `display:none` to checking for height and width 0 -- and they didn't even do a recursive search for display=none, as is done in this branch.
http://docs.jquery.com/Release:jQuery_1.3.2#:visible.2F:hidden_Overhauled