The loop test can be quite slow, specially on computers without
cryptography-friendly instructions.
This patch introduces a new flag for testing, so that we can bring the
threshold down to 5. The test is just as useful but now runs in a few
seconds, as opposed to a few minutes.
glog works fine and has great features, but it does not play along well
with systemd or standard log rotators (as it does the rotation itself).
So this patch replaces glog with a new logging module "log", which by
default logs to stderr, in a systemd-friendly manner.
Logging to files or syslog is still supported.
The default INFO logs are more oriented towards debugging and can be
a bit too verbose when looking for high-level information.
This patch introduces a new "maillog" package, used to log messages of
particular relevance to mail transmission at a higher level.
This patch implements some measures against email loops, such as keeping
a limit on the lenght of an address, and rejecting email that has too
many Received headers.
It's not perfect (a server could be actively removing Received headers),
but it should cover the normal accidents and misconfigurations.
