[whatwg] Quirks mode handling of rowspan="0"

[Boris Zbarsky]

Per HTML5 spec, rowspan="0" should span to the end of the table section.

WebKit seems to not implement this at all.

Opera implements this in quirks and standards mode.

Gecko implements this in standards mode only; in quirks mode, 
rowspan="0" is treated like rowspan="1".  When we last tried to do the 
"right" thing in quirks mode, back in 2003 or so, we ran into site 
compatibility issues, hence the current setup.

I don't know what Trident does here; worth testing.

In any case, my suggestion is that in quirks mode, rowspan="0" not be 
supported.

-Boris