Assign correct source to parser while rt-testing.

* RT testing reparses wikitext produced by serialization.  But, it
  was setting src wikitext to *original* wikitext rather than
  *serialized* wikitext which messed up source-substring based
  extraction in parser and thus showed spurious semantic diffs
  where none existed.
* This fix reclassifies all previously reported semantic errors on
  en:Aberdeen F C seasons as syntactic errors.

Change-Id: Icb4b1522cdeb50ff1cd5872c793cb58c87d6b7b9