Use better variable name in CoreParserFunctions::pagesize()

Also moved the retrieval of the revision ID near the one of the
page ID so that the call of ParserOutput::addTemplate() is much
clearer than the actual one.

Change-Id: Ie71ee76e90cc131eac25c0f339d5250d5163ce2e
Merge "Use better variable name in CoreParserFunctions::pagesize()"