Found a MUCH better way to store the UIDL's of

Found a MUCH better way to store the UIDL's of
previously seen remote POP3 messages.  The first attempt
involved another directory full of crap, lots of reading,
writing, and parsing of yet another file format, and a bunch
of extra code involving linked lists and string comparisons
and after several days it still didn't work.  This new version
leverages the S_USETABLE database, uses about 50 lines of new
code, and I got it working in about 20 minutes.  Sometimes
you've just got to take a couple of steps back and rethink
things.