limit user session data (HomePageHandle and auth_dbi have to invalidated anyway)

limit user session data (HomePageHandle and auth_dbi have to invalidated anyway)
  because they will not survive db sessions, if too large.
extended action=upgrade
some WikiTranslation button work
revert WIKIAUTH_UNOBTAINABLE (need it for main.php)
some temp. session debug statements

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@3420 96ab9672-09ca-45d6-a79d-3d69d39ca109