[Nmh-workers] POP cleanup - old crap

[Ken Hornstein]

I'm cleaning out the last vestiges of KPOP support (which already doesn't
work), and I've found a few extra things.  In the interests of trying to
remove the giant maze of #ifdefs that the POP code currently is, I'm
wondering about:

- RPOP (POP from a local reserved port).  I asked about this before, and
  no on objected.
- APOP.  Do people still use this?  CRAM-MD5 via SASL is better, and I'm
  not seeing newer POP clients which claim to support APOP.  I think the
  world has moved on here.
- MPOP.  Not even sure _what_ this is.
- NNTP.  Yes, there is some weird bboards support which talks via NNTP.
  It complicates the code greatly, and I wonder if anyone still uses it.
  Can we ditch it?

BTW, when going through the nmh code, I found the -proxy switch, which
I think does what Michael Richardson asked about (runs a command and lets
you talk to that to speak POP).  Well, it might not be exactly what he
wanted, but it's probably a good start.

--Ken