refactor session_key (__errorurl) to handle cases where the form is generated throuhg an ajax call: in case of an entity form, return the entity's absolute url. Also allow to force session key value

#! /bin/sh -e
 
case "$1" in
    purge)
        rm -rf /etc/cubicweb.d/
    	rm -rf /var/run/cubicweb/
	rm -rf /var/log/cubicweb/
	rm -rf /var/lib/cubicweb/
    ;;
esac
 
#DEBHELPER#
 
exit 0