Dump some useless calls to dhclient-script. i.e. MEDIUM, PREINIT,

ARPSEND, ARPCHECK. Drop support for 'media', 'medium' and 'alias'
specifications in dhclient.conf. Old leases still parse but these
options now have no effect.
Be more polite and decline all offers we don't accept. Fix a IMSG
length check.
Many expressions of support at various bars.
ok henning@ deraadt@ beck@

src/etc/dhclient.conf

@@ -1,4 +1,4 @@
-# $OpenBSD: dhclient.conf,v 1.1 1998/09/08 20:26:41 marc Exp $
+# $OpenBSD: dhclient.conf,v 1.2 2011/04/04 11:14:52 krw Exp $
 #
 # DHCP Client Configuration
 #
@@ -14,4 +14,3 @@
 # request subnet-mask, broadcast-address, time-offset, routers,
 #	domain-name, domain-name-servers, host-name, lpr-servers, ntp-servers;
 # require subnet-mask, domain-name-servers, routers;
-# media "link0 link1", "link0 link1", "link0 link1", "-link0 link1";