The new mail500: first version

[Julio Sánchez Fernández <j_sanchez@stl.es>]

Alright, I have just committed the new mail500 to the HEAD branch.

Please don't trust this at all.  It is close to start doing what I want.
It has had *some* testing in my environment with the mail model I use
and it is still unstable.  It has had *no* testing with other mail models.
It is likely to create mail loops, miss recipients without an error bounce
and, if it feels like bouncing a message, it is likely to be misleading or
wrong.  The original code had some areas for buffer overruns and unchecked
memory allocations.  I have not removed any of these problems and I have
introduced others.

Really, I mean it.  This is intended to foster feedback and further
development.  If you were using mail500 before, stick to the old versions
for the time being.

In addition to the major instabilities introduced above, many things that
were supported before are broken now:  onVacation, moderator and other
things are broken.  Mailing to group-members does not work anymore (is this
needed?  It seemed like an internal artifact...).

The man page has not been updated, but I have updated parts of the README
file, that's all the documentation there is, besides the source code itself.

Feedback is welcome.

Julio