[CSS21] table-caption width

So the spec currently says that the anonymous table box (the table caption's
containing block) has the same width as the border box of the table.
Unfortunately, this causes the table caption to overflow in cases where its
contents are wider than the border box.

I think it would be better to say that the anonymous table box is as wide
as max(table-width, table-caption-min-intrinsic-width).

Testcase:
   http://lists.w3.org/Archives/Public/www-archive/2010Jun/att-0015/table-caption-004.xht
(I think Firefox has the behavior we want.)

~fantasai