DOM Fragment unpacking: Deal with some more nested a-tag ugliness

* When nested-a-tag-generating wikitext shows up in a template,
  it spells trouble. The nested a-tag will break up into multiple
  a-tags and the dom-fragment unpacker has to make sure that this
  doesn't break up encapsulation by adding about-ids appropriately
  after the split.

* {{echo|[[Foo|This is [[bad]], very bad]]}}

  Before this patch, this snippet would RT as:
  {{echo|[[Foo|This is [[bad]], very bad]]}}[[bad]], very bad

  The reason is because when the link text is processed in its
  own pipeline and the fragment is unpacked, the wikitext is
  effectively {{echo|[[Foo|This is ]][[bad]], very bad}}. So,
  the unpacker has to make sure that the pieces of the original
  link text that moved up one level have encapsulation about
  ids as well.

* Fixes RT errors on es:Almeriapedia and he:מרים_רות

Change-Id: Id685d333f78ea8cd230a6911a4898c63e812f080