* changed stored pref representation as before.

* changed stored pref representation as before.
  the array of objects is 1) bigger and 2)
  less portable. If we would import packed pref
  objects and the object definition was changed, PHP would fail.
  This doesn't happen with an simple array of non-default values.
* use $prefs->retrieve and $prefs->store methods, where retrieve
  understands the interim format of array of objects also.
* simplified $prefs->get() and fixed $prefs->set()
* added $user->_userid and class '_WikiUser' portability functions
* fixed $user object ->_level upgrading, mostly using sessions.
  this fixes yesterdays problems with loosing authorization level.
* fixed WikiUserNew::checkPass to return the _level
* fixed WikiUserNew::isSignedIn
* added explodePageList to class PageList, support sortby arg
* fixed UserPreferences for WikiUserNew
* fixed WikiPlugin for empty defaults array
* UnfoldSubpages: added pagename arg, renamed pages arg,
  removed sort arg, support sortby arg

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@2959 96ab9672-09ca-45d6-a79d-3d69d39ca109