[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
# some entities have been added before schema entities, fix the 'is' and
# 'is_instance_of' relations
for rtype in ('is', 'is_instance_of'):
sql('INSERT INTO %s_relation '
'SELECT X.eid, ET.cw_eid FROM entities as X, cw_CWEType as ET '
'WHERE X.type=ET.cw_name AND NOT EXISTS('
' SELECT 1 from is_relation '
' WHERE eid_from=X.eid AND eid_to=ET.cw_eid)' % rtype)