change macro expansion character from $ to \001 so that $'s can be

change macro expansion character from $ to \001 so that $'s can be
used in headers -- the .cf file is unchanged by mapping $ to \001.
\001 is now a manifest constant.

SCCS-vsn: usr.sbin/sendmail/src/macro.c 4.2
SCCS-vsn: usr.sbin/sendmail/src/queue.c 4.2
SCCS-vsn: usr.sbin/sendmail/src/headers.c 4.4
SCCS-vsn: usr.sbin/sendmail/src/main.c 4.8
SCCS-vsn: usr.sbin/sendmail/src/deliver.c 4.6
SCCS-vsn: usr.sbin/sendmail/src/sendmail.h 4.4
SCCS-vsn: usr.sbin/sendmail/src/savemail.c 4.3
SCCS-vsn: usr.sbin/sendmail/src/srvrsmtp.c 4.7
SCCS-vsn: usr.sbin/sendmail/src/alias.c 4.3
SCCS-vsn: usr.sbin/sendmail/src/envelope.c 4.3
SCCS-vsn: usr.sbin/sendmail/src/parseaddr.c 4.4
SCCS-vsn: usr.sbin/sendmail/src/usersmtp.c 4.9
SCCS-vsn: usr.sbin/sendmail/src/readcf.c 4.4