implement alias owner feature. this actually works for any user.

implement alias owner feature.  this actually works for any user.
basically, if the alias owner-xxx exists, errors sending to xxx will be
sent to that alias rather than to the sender.

SCCS-vsn: usr.sbin/sendmail/src/deliver.c 3.82
SCCS-vsn: usr.sbin/sendmail/src/sendmail.h 3.72
SCCS-vsn: usr.sbin/sendmail/src/savemail.c 3.32
SCCS-vsn: usr.sbin/sendmail/src/version.c 3.113
SCCS-vsn: usr.sbin/sendmail/src/main.c 3.79
SCCS-vsn: usr.sbin/sendmail/src/srvrsmtp.c 3.16
SCCS-vsn: usr.sbin/sendmail/src/queue.c 3.18