Allow to specify a hostname on relay rule:

        accept ... relay hostname "foobar"

Tweak the on-disk envelope format a bit, but make update seamless
for existing envelopes.
Remove the dead code path for passing incoming message data through the mfa.
It is not going to be done that way.
Internal update for the upcoming filter infrastructure:
- use log.c
- pass filter name to filter process
- various API improvements
Allow the construction of filterchains as a sequence of individual filters
and or other filterchains.
missing include
include the right header...
More changes in the filter framework/API.
Add code to eventually pass the message content through the mfa.
The mfa will get the output message fd from the queue, setup a filter
chain for the content, and send the filter input socket to the smtp
process.

This is not plugged for now.
add missing header and fix format string
Return EX_TEMPFAIL while enqueued offline.
Fix exit codes to confirm to sendmail(8).
Merge pull request #337 from snimmagadda/301

Fix exit codes to match sendmail(8)
Implement smtpctl encrypt subcommand.
do not leak imsg structure in mta and smtp processes
previous commit was not right, fix for real this time
fix memory leak in lookup process
Fix a bug that lead to leaking mfa sessions.
When building the expansion tree, distinguish between apparently
identical nodes that appear in different contexts.  The same delivery
can happen for different users, or as a different destination address.

Fixes a bug with setups like the following, where a mail sent to
contact@foo.net was not delivered to both /tmp/me and /tmp/she.

table foobar { me@foo.net = vmail, she@foo.net = vmail, \
	       contact@foo.net = "me@foo.net,she@foo.net" }
accept for domain foo.net virtual <foobar> \
	deliver to maildir "/tmp/%{dest.user}"
remove dead debugging code
K_USERINFO strings have only 3 parts