[dovecot] inetd/xinetd/tcpserver support

[Timo Sirainen]

I was just thinking how they could be easily supported. This would work,
right? :

imap stream tcp nowait root /usr/sbin/tcpd /usr/local/libexec/dovecot/imap-login
imaps stream tcp nowait root /usr/sbin/tcpd /usr/local/libexec/dovecot/imap-login --ssl

imap-login would try to connect to master process using some named
socket. If it couldn't, it would create the master process itself.
Master process would work as usual (executes auth and imap processes),
except it wouldn't be executing login processes.

This wouldn't require much code changing, and it would still be using
all the same privilege separations as the standalone version so it would
be just a secure.

Only thing I'm wondering is if any of the TCP wrappers care about the
created child processes? The master process would have to stay alive
after the connection that created it dies.

I guess I'll implement this soon and try if it works.