fix support for tls+backup://
last known msgbuf_write vs EOF fix (by krw@)
Make sure the correct errno is reported by warn* or err* and not
the errno of an intervening cleanup operation like close/unlink/etc.

Diff from Doug Hogan (doug (at) acyclic.org)
Use getlogin() to determine real user name where possible.
Commit by millert@, OK guenther@ deraadt@
missing errno
some MUAs will not only bypass the local enqueuer, but also forget to
strip the BCC header when sending the DATA part of the SMTP transaction.

force smtp sessions to ignore these headers
Fixes a typo in trace options: filter(s)