Prevent PDF table rows from inheriting @rowsep from previous row #1486

Please try this out before merging it if you have the chance. You can use [this Gist](https://gist.github.com/emth/6368345) if you want. `tables.xsl` is pretty mystifying in places (and certainly could use an XSLT2.0 rewrite), but I *think* I got it right.