added filter option to events
refactored ar_pinp::getCallback to use a Closure
made sure that event callbacks can only call templates or Closures
fixed getCallback() case in events.php and html/form.php


git-svn-id: https://svn.muze.nl/svn/ariadne-php5/trunk@6618 7882d7ee-46e0-0310-a255-a28a61b628e4