run SMTP jobs in a subprocess so that multiple jobs will work. This

run SMTP jobs in a subprocess so that multiple jobs will work.  This
delta also changes the envelope data structure so that flags are in
a bit map, and adjusts some of the semantics.  The transcript is now
local to an envelope.  A bunch of old code is deleted.  A serious bug
was fixed in the "run in background" code.  Etc., etc.

SCCS-mr: usr.sbin/sendmail/src/main.c 026
SCCS-mr: usr.sbin/sendmail/src/deliver.c 026
SCCS-mr: usr.sbin/sendmail/src/err.c 026
SCCS-mr: usr.sbin/sendmail/src/sendmail.h 026
SCCS-mr: usr.sbin/sendmail/src/savemail.c 026
SCCS-mr: usr.sbin/sendmail/src/version.c 026
SCCS-mr: usr.sbin/sendmail/src/queue.c 026
SCCS-mr: usr.sbin/sendmail/src/srvrsmtp.c 026
SCCS-mr: usr.sbin/sendmail/src/recipient.c 026
SCCS-mr: usr.sbin/sendmail/src/usersmtp.c 026
SCCS-mr: usr.sbin/sendmail/src/readcf.c 026
SCCS-mr: usr.sbin/sendmail/src/headers.c 026
SCCS-vsn: usr.sbin/sendmail/src/main.c 3.139
SCCS-vsn: usr.sbin/sendmail/src/deliver.c 3.131
SCCS-vsn: usr.sbin/sendmail/src/err.c 3.34
SCCS-vsn: usr.sbin/sendmail/src/sendmail.h 3.101
SCCS-vsn: usr.sbin/sendmail/src/savemail.c 3.48
SCCS-vsn: usr.sbin/sendmail/src/version.c 3.251
SCCS-vsn: usr.sbin/sendmail/src/queue.c 3.52
SCCS-vsn: usr.sbin/sendmail/src/srvrsmtp.c 3.37
SCCS-vsn: usr.sbin/sendmail/src/recipient.c 3.47
SCCS-vsn: usr.sbin/sendmail/src/usersmtp.c 3.27
SCCS-vsn: usr.sbin/sendmail/src/readcf.c 3.46
SCCS-vsn: usr.sbin/sendmail/src/headers.c 3.38