Add "strip extra cc's if they already exist on the list" filter

[GoogleCodeExporter]

strip recipients from the CC header if explicitly named recipients are members
of the list. cuts down on duplicates and traffic. probably should be implemented
as a plugin.

Jon, if you want it, you get to write it.

Original issue reported on code.google.com by lhori...@gmail.com on 4 Jun 2009 at 10:39