[selectors, facet] make is_instance and other EClassSelector subclass gather entity classes from 'select' and 'filtered_variable' context information. Closes #1796732 This allow for instance to use the filter form on rqlst where the filtered variable is not selected

usr/lib/python2.4/site-packages/cubicweb/
etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances