motd needs to be re-generated when DISTRIBVER changes, so change he

Makefile to use the new ${_NETBSD_VERSION_DEPENDS} mechanism defined in
bsd.own.mk.

Rename the default motd file in the source tree from "motd" to
"motd.default", because otherwise it would conflict with the motd file
that is now created in the .OBJDIR.

etc/Makefile

@@ -1,4 +1,4 @@
-#	$NetBSD: Makefile,v 1.399 2012/11/04 11:04:10 apb Exp $
+#	$NetBSD: Makefile,v 1.400 2012/11/04 11:09:14 apb Exp $
 #	from: @(#)Makefile	8.7 (Berkeley) 5/25/95
 
 # Environment variables without default values:
@@ -114,21 +114,8 @@ BIN1+=	etc.${MACHINE}/ttyaction
 .endif
 
 # -rw-rw-r--
-.if !empty(DISTRIBVER:M*.99.*)
-BIN2+=	motd.current
-FILESNAME_motd.current=	motd
-.elif !empty(DISTRIBVER:M*BETA*)
-BIN2+=	motd.beta
-FILESNAME_motd.beta=	motd
-.elif !empty(DISTRIBVER:M*RC*)
-BIN2+=	motd.rc
-FILESNAME_motd.rc=	motd
-.elif !empty(DISTRIBVER:M*STABLE*)
-BIN2+=	motd.stable
-FILESNAME_motd.stable=	motd
-.else
 BIN2+=	motd
-.endif
+FILESBUILD_motd=	YES
 
 # -rw-------
 BIN3+=	hosts.equiv
@@ -172,6 +159,24 @@ distribution: .PHONY .MAKE check_DESTDIR distrib-dirs
 .endif	# !DISTRIBUTION_DONE
 
 
+# motd is copied from a different ${MOTD_SOURCE} depending on DISTRIBVER
+#
+.if !empty(DISTRIBVER:M*.99.*)
+MOTD_SOURCE=	motd.current
+.elif !empty(DISTRIBVER:M*BETA*)
+MOTD_SOURCE=	motd.beta
+.elif !empty(DISTRIBVER:M*RC*)
+MOTD_SOURCE=	motd.rc
+.elif !empty(DISTRIBVER:M*STABLE*)
+MOTD_SOURCE=	motd.stable
+.else
+MOTD_SOURCE=	motd.default
+.endif
+CLEANFILES+= motd
+motd: ${.CURDIR}/${MOTD_SOURCE} ${_NETBSD_VERSION_DEPENDS}
+	${_MKTARGET_CREATE}
+	${HOST_INSTALL_FILE} ${.CURDIR}/${MOTD_SOURCE} ${.TARGET}
+
 CLEANFILES+=	MAKEDEV
 MAKEDEV: ${.CURDIR}/MAKEDEV.awk ${.CURDIR}/MAKEDEV.tmpl \
     ${.CURDIR}/etc.${MACHINE}/MAKEDEV.conf