(Bug 52430) Accept non-standard WS in extension tags: continued

* Commit c55b629c added support for accepting non-standard WS
  in xmlish tags and added a parser test for <ref> tags. However,
  non-ref extension tags still had broken support. This patch
  fixes that.

  Ex: <math >1+2</math > now RTs without introducing an extra
  closing </math> tag.

* zhwiki:%E4%BD%9C%E7%94%A8%E9%87%8F-%E8%A7%92%E5%BA%A6%E5%9D%90%E6%A0%87
  now RTs without a semantic error, just a syntactic diff around
  normalizing the whitespace in "</math >".

* FIXME: Not sure how to add a parser test for this yet.

Change-Id: Icbd236d8f6902359b9fab453b80aec81a878e399
Merge "(Bug 52430) Accept non-standard WS in extension tags: continued"