fixed bug which could cause some page's stage not to be set before filtering
fixed bug which could cause some page's stage not to be set before filtering

--HG--
extra : convert_revision : svn%3A177060d3-6165-4ab0-95eb-642399a075a8/nanoc/trunk%40400

barraq/nanoc,RubenVerborgh/nanoc,remko/nanoc,hilohiro/nanoc,legallybrown/nanoc,gjtorikian/nanoc,nanoc/nanoc