This handles row and colspans. Partially addresses #6344.
It also ensures that cells won't wrap text in places where it
wouldn't normally wrap, even if this means making the cells wider
than requested by the colspec. (Closes#9001. Closes 7641.)
Parameters are different, so this is a breaking [API change].
Markdown, RST, and Muse writers have been adjusted to
use the new `gridTable`.
John MacFarlane
01257ef6eb
