More precise check for possible changes in text nodes

* In rt mode (editMode === false), we can extrapolate dsr

* We don't diff when selser is disabled, so don't assume nothing has changed
  then.

* New blacklist entries. These are phantom failures that are caused by changed
  plain serializer output we are comparing with. This has bitten us a few
  times recently, and we should really look for a way to directly simulate
  edits on the original wikitext instead without using the plain (non-selser)
  serializer.

Change-Id: Idd17d6b40cde8ec870878a91105aa9711f223610