wymEqual tests against unparsed HTML by default.

This is the jewl of this PR. It seems to me like a flaw of the `mergeRow` method, which was covered over by the parser, making the test pass.

I didn't grasp the whole of the logic in the `mergeRow` method, but I'm quite sure that `append`ing a cell inside another cell is *not* what we desire.

The change to `after` makes the test pass and doesn't make any other test fail. So I can guess that this is the desired behavior.

Some manual testing reveals that row merging isn't all that stable, anyway, as I can make it mutilate a table very easily, just the same in `master` and in this branch.