* revert to the wikidb ref passing. there's no memory abuse there.

* revert to the wikidb ref passing. there's no memory abuse there.
* use new wikidb->_cache->_id_cache[] instead of wikidb->_iwpcache, to effectively
  store page ids with getPageLinks (GleanDescription) of all existing pages, which
  are also needed at the rendering for linkExistingWikiWord().
  pass options to pageiterator.
  use this cache also for _get_pageid()
  This saves about 8 SELECT count per page (num all pagelinks).
* fix passing of all page fields to the pageiterator.
* fix overlarge session data which got broken with the latest ACCESS_LOG_SQL changes

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@4117 96ab9672-09ca-45d6-a79d-3d69d39ca109