internal package Foswiki::Prefs::Request 
Support setting topic preferences when saving a topic.
URL parameters are parsed and * Set commands extracted and
used to update settings in the topic on the fly, usually during
a topic save.
Parameters have the form:
http://....?[Local|Set|Unset|Default]+<key>=<value>
  
Given a Foswiki request and a 
Foswiki::Meta object, identify and parse
parameters in the request and use them to set corresponding
preferences in the meta object.