finish implementing envelopes. it's not completely clear to me that

finish implementing envelopes.  it's not completely clear to me that
this is really the way to go, but it seems clearly better than what
i had before.  this delta includes many other minor changes, so it
should probably not be blithely removed.

SCCS-vsn: usr.sbin/sendmail/src/alias.c 3.32
SCCS-vsn: usr.sbin/sendmail/src/deliver.c 3.80
SCCS-vsn: usr.sbin/sendmail/src/collect.c 3.39
SCCS-vsn: usr.sbin/sendmail/src/sendmail.h 3.70
SCCS-vsn: usr.sbin/sendmail/src/parseaddr.c 3.42
SCCS-vsn: usr.sbin/sendmail/src/savemail.c 3.30
SCCS-vsn: usr.sbin/sendmail/src/version.c 3.108
SCCS-vsn: usr.sbin/sendmail/src/main.c 3.76
SCCS-vsn: usr.sbin/sendmail/src/readcf.c 3.25
SCCS-vsn: usr.sbin/sendmail/src/macro.c 3.12
SCCS-vsn: usr.sbin/sendmail/src/headers.c 3.19
SCCS-vsn: usr.sbin/sendmail/src/usersmtp.c 3.10
SCCS-vsn: usr.sbin/sendmail/src/queue.c 3.14