change the send queue to be only one queue instead of one per mailer.

change the send queue to be only one queue instead of one per mailer.
this is slightly inefficient but simpler.  also, pass this queue
around so we can have multiple send queues.  this makes VRFY work.

SCCS-vsn: usr.sbin/sendmail/src/alias.c 3.27
SCCS-vsn: usr.sbin/sendmail/src/sendmail.h 3.54
SCCS-vsn: usr.sbin/sendmail/src/parseaddr.c 3.35
SCCS-vsn: usr.sbin/sendmail/src/version.c 3.65
SCCS-vsn: usr.sbin/sendmail/src/main.c 3.54
SCCS-vsn: usr.sbin/sendmail/src/srvrsmtp.c 3.10
SCCS-vsn: usr.sbin/sendmail/src/readcf.c 3.17
SCCS-vsn: usr.sbin/sendmail/src/headers.c 3.11
SCCS-vsn: usr.sbin/sendmail/src/recipient.c 3.30
SCCS-vsn: usr.sbin/sendmail/src/queue.c 3.5
SCCS-vsn: usr.sbin/sendmail/src/deliver.c 3.55