Fix form based wt parsing

 * When a page name and oldid were present, the wt was being set to the
   entire page source.

 * Also renames some function to be clearer about what they do.

 * And moves setting the pageSrcInfo to before logging "starting
   parsing" so that the oldid is present when available. Ex.

     [info][mediawikiwiki/Parsoid] started parsing
     [info][mediawikiwiki/Parsoid?oldid=1183568] completed parsing

     vs

     [info][mediawikiwiki/Parsoid?oldid=1183568] started parsing
     [info][mediawikiwiki/Parsoid?oldid=1183568] completed parsing

Change-Id: I7a2a2523ed436b0588c33b7b8f5004c602d5f482