Our non-delivery status notifications are quite simple today, but that
makes it much more difficult to support internationalization and
cross-language reporting.
There is a standard for internationalized DSNs, RFC 6533 (which builds
on top of the structured DSNs from RFC 3464).
This patch changes our DSN messages to be based on those standards, so
it is easier for MUAs to display reports according to the users'
languages preferences.
Note we still use message/rfc822 + 8bit to transmit the message, instead
of message/global, for compatibility reasons. This seems to be more
universally compatible, but the decision might be revisited in the
future. See RFC 5335 (section 4.6 in particular).
The nc.py script is only used in a single test, and for waiting for a
TCP port to be opened for listening.
This patch replaces it entirely, by using chamuyero for the test, and
bash for waiting on a TCP port.
