generally more PHPDOC docs

generally more PHPDOC docs
  see http://xarch.tu-graz.ac.at/home/rurban/phpwiki/xref/
fxied WikiUserNew pref handling: empty theme not stored, save only
  changed prefs, sql prefs improved, fixed password update,
  removed REPLACE sql (dangerous)
moved gettext init after the locale was guessed
+ some minor changes

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@3090 96ab9672-09ca-45d6-a79d-3d69d39ca109