IMAP and NNTP server threads don't exit on window close, because they're
referenced by main thread and no particular window thread is entitled
to close them.

Need to look at reference counting.  Message window objects aren't
getting counted out, maybe others likewise.  I think this is most
likely a problem in the C++ modules, not here, but anyway.  Would
make it easier to deal other resources, e.g. files.

Configuration interface.
Edit the old/new ranges in a newsgroup.
Edit the list of IMAP folders.
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crash after Quit(), during C++ delete (~MenuItem from menu bar?)
Doesn't notice menubar menu options.
