Organize queue_proc.c code as other queue backends.
update the queue backend API to only define an init call and get rid of the
QOP_* defines.  Builtin backends use the same API as external ones to
register their callback.
Merge branch 'master' into portable

Conflicts:
	smtpd/queue_proc.c
fix closefrom(2) call
Merge branch 'portable' of https://github.com/poolpOrg/OpenSMTPD into portable