avoid storing transient state in pagestate

avoid storing transient state in pagestate

None of the comment state needs to be stored through the a later run of
ikiwiki, so move it all from pagestate to a more transient storage.

This is assuming that we'll never want to add pagespecs to search against
the comment state. Pagespecs like author() are why the meta plugin does
store its meta data in pagestate -- the data can be needed later to match
against.