Re: colgroup span clarification (PR#7829)

We have implemented your change as proposed.

> The current wording is suggests that the span attribute should be
> ignored more often than was intended.
> 
> At http://www.w3.org/TR/xhtml2/mod-tables.html#sec_29.2.
> Please change:
> """
> User agents must ignore this attribute if the colgroup element
> contains one or more col elements.
> """
> into something more like:
> """
> User agents must ignore this attribute's value on a colgroup element
> if that colgroup contains one or more col elements.  Instead, the
> value must be computed by summing the span attributes of the enclosed
> col elements.
> """
> 
> -jJ
> 
>