Massive overhaul of networking code. Changes:

Massive overhaul of networking code.  Changes:

- All networking interfaces now converted to new APIs (getaddrinfo() and
  the like).  All networking now supports IPv6 (with the exception of
  the built-in FTP client).
- SASL security layers are now supported for SMTP.
- Command-line and profile-based selection of the SMTP server and port.