reduce number of instances of CurEnv by passing it as a parameter

reduce number of instances of CurEnv by passing it as a parameter

SCCS-vsn: usr.sbin/sendmail/src/stats.c 5.12
SCCS-vsn: usr.sbin/sendmail/src/headers.c 5.20
SCCS-vsn: usr.sbin/sendmail/src/usersmtp.c 5.23
SCCS-vsn: usr.sbin/sendmail/src/recipient.c 5.33
SCCS-vsn: usr.sbin/sendmail/src/main.c 5.53
SCCS-vsn: usr.sbin/sendmail/src/envelope.c 5.28
SCCS-vsn: usr.sbin/sendmail/src/parseaddr.c 5.20
SCCS-vsn: usr.sbin/sendmail/src/collect.c 5.12
SCCS-vsn: usr.sbin/sendmail/src/version.c 5.106
SCCS-vsn: usr.sbin/sendmail/src/savemail.c 5.18
SCCS-vsn: usr.sbin/sendmail/src/srvrsmtp.c 5.35
SCCS-vsn: usr.sbin/sendmail/src/readcf.c 5.41
SCCS-vsn: usr.sbin/sendmail/src/deliver.c 5.60
SCCS-vsn: usr.sbin/sendmail/src/queue.c 5.43
SCCS-vsn: usr.sbin/sendmail/src/conf.c 5.40
SCCS-vsn: usr.sbin/sendmail/src/alias.c 5.34
SCCS-vsn: usr.sbin/sendmail/src/udb.c 5.19