* Changed my mind about the on-disk format for wiki history. DELETE ANY WIKI ROOMS...

* Changed my mind about the on-disk format for wiki history.  DELETE ANY WIKI ROOMS YOU MAY HAVE ALREADY CREATED.  We now do wiki history backwards.  In other words, the diffs in each part would be applied top to bottom in order to revert to older and older versions.  Theoretically if you apply them all the way through you would end up with an empty page.  This will allow revision control to work properly even with a partial history.