Use BSMTP response code; misc cleanups
Use BSMTP response code; misc cleanups

Exim's BSMTP interface will indicate the SMTP response to the exchange;
actually use it rather than assuming all errors are 400-class soft ones.

Tolerate $transaction->header returning undef (since it evidently can under
some conditions).

Convert a few errant tabs to spaces.

Fix vi modeline.

Signed-off-by: Robert <c9484850f6ee3d3fb73f3c3345f26ec064da35e4@pobox.com>

msimerson/qpsmtpd,sieutruc/qpsmtpd,msimerson/qpsmtpd,priyadi/qpsmtpd,smtpd/qpsmtpd,priyadi/qpsmtpd,smtpd/qpsmtpd,salvis/qpsmtpd,sieutruc/qpsmtpd,salvis/qpsmtpd,priyadi/qpsmtpd,sieutruc/qpsmtpd