Load balance listener instances

Currently Esper calls all listener instances of an EPStatement, instead of load balancing the calls to the listener instances.
If the calls are load balanced then:
1. User would provide the list of listener objects for an EPStatement which Esper would maintain in a pool, for each of such statements.
2. Whenever match(es) occur for that statement, Esper would call one or multiple listener instance(s) from the pool and hence reuse the listener instances concurrently.

Mailing list discussion: http://archive.esper.codehaus.org/user/507053.14107.qm%40web37107.mail.mud.yahoo.com