I think filterworker.rb goes away in logstash 1.2/master

Replaced by this:
* https://github.com/logstash/logstash/blob/master/lib/logstash/pipeline.rb#L165-L191
* https://github.com/logstash/logstash/blob/master/lib/logstash/config/config_ast.rb#L59-L79

The new pipeline allows events to be created in the middle of a filter set and only be processed by filters occuring afterwards.