These options are to attempt to address the issue (#178) reported by Michael J. Ryan
with regards to a Thunderbird error:
"Sending of the messages failed. You can only send to one news server at a time."
when attempting to reply to a message that was posted to multiple newsgroups,
but the server has not actually advertised that it serves that newsgroups (because
it doesn't or the names a different than one the server uses for the same area).

-force will force the export "Newsgroups" header field to contain only the name
of the locally selectec newsgroup.
-filter will remove any Newsgroup names from the exported "Newsgroups" header
if they don't exist on the local server.