linuxrc: call ensure_initramfs_mounts after mounting ${REAL_ROOT}

This makes possible to deal with systemd and separate /usr support
as discussed in bug #479730.

defaults/linuxrc

@@ -443,14 +443,32 @@ do
 		# else not a good root and start over.
 		if [ "$?" = '0' ]
 		then
-			if [ -d ${NEW_ROOT}/dev -a -x "${NEW_ROOT}${REAL_INIT:-/sbin/init}" ] || [ "${REAL_ROOT}" = "/dev/nfs" ]
-			then
+			# now that the root filesystem is mounted, before
+			# checking the validity of ${NEW_ROOT} and ${REAL_INIT},
+			# ensure that ${NEW_ROOT}/etc/initramfs.mounts entries
+			# are mounted.
+			ensure_initramfs_mounts
+
+			# NFS does not need further checks here.
+			if [ "${REAL_ROOT}" = "/dev/nfs" ]; then
 				break
-			else
-				bad_msg "The filesystem mounted at ${REAL_ROOT} does not appear to be a valid /, try again"
-				got_good_root=0
-				REAL_ROOT=''
 			fi
+
+			if [ ! -d "${NEW_ROOT}/dev" ]; then
+				_msg="The filesystem ${REAL_ROOT},"
+				_msg="${_msg} mounted at ${NEW_ROOT}"
+				_msg="${_msg} does not contain /dev"
+				_msg="${_msg}, init will likely fail..."
+				bad_msg "${_msg}"
+			fi
+			if [ ! -x "${NEW_ROOT}${REAL_INIT:-/sbin/init}" ]; then
+				_msg="The filesystem ${REAL_ROOT},"
+				_msg="${_msg} mounted at ${NEW_ROOT}"
+				_msg="${_msg} does not contain a valid"
+				_msg="${_msg} init=${REAL_INIT}"
+				bad_msg "${_msg}"
+			fi
+			break
 		else
 			bad_msg "Could not mount specified ROOT, try again"
 			got_good_root=0
@@ -648,7 +666,8 @@ then
 	CDBOOT=1
 fi
 
-# Mount the additional things as required by udev & systemd
+# Re-run this here, which makes sure that it at least had a chance
+# to be called.
 ensure_initramfs_mounts
 
 splashcmd hasroot "${NEW_ROOT}"