Various small changes

* Compacter kicks in too early, potentially stripping columns (in this case:
  rev_parent_id) that are used for the callback to check if index needs to be created or
  merged. Compact later, when saving to cache.
* I didn't manage to get Parsoid's _wikitext test form running, but wikitext to HTML
  doesn't even need Parsoid; MW parser can do that (and unless the HTML to wikitext
  conversion will also be needed, we should probably not add a dependency on Parsoid)

Change-Id: I2d64d70a81e887a850403a42bafd9d888a0fac85