poplib module is currently lacking a test suite which actually connects
to a server and uses the POP3 class methods and facilities.
Bug #3727, discovered just a bunch of days before the stable release of
Python 3.0 is an example of how much a test suite is necessary.

As done in #3939 for the ftplib module, in attachment I provide a test
suite which implements an asyncore-based dummy POP3 server which sends
fixed response codes that I used to test all the relevant POP3 class
methods.
Tests for the POP3_SSL class are also included.
Although not that useful (IMHO) I didn't remove the old tests about
timeouts.

Tested successfully against Python 2.6 on Windows XP SP3, Debian Etch
and FreeBSD 7.0.