CAY-1819  When adding a filter, auto-register it as a listener

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1484110 13f79535-47bb-0310-9956-ffa450edef68
seemed like dead code?

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1484111 13f79535-47bb-0310-9956-ffa450edef68
CAY-1819  When adding a filter, auto-register it as a listener

use new feature in unit tests

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1484112 13f79535-47bb-0310-9956-ffa450edef68