make it easier to use a custom mirror

live-build/auto/config

@@ -1,21 +1,21 @@
 #! /bin/sh
 set -e
 
-MIRROR=
-case $(hostname --fqdn) in
-	bld-*.mmjgroup.com)	;;
-	*.mmjgroup.com)
-		case $ARCH in
-			i386|amd64)	MIRROR=http://archive.mmjgroup.com/ubuntu/ ;;
-			*)		MIRROR=http://archive.mmjgroup.com/ubuntu-ports/ ;;
-		esac
-		;;
-	*.0c3.net)		MIRROR=http://ftp.iinet.net.au/linux/ubuntu/ ;;
-	*.ubuntu.com)		MIRROR=http://ftpmaster.internal/ubuntu/ ;;
-	*.warthogs.hbd.com)	MIRROR=http://ftpmaster.internal/ubuntu/ ;;
-	*.buildd)		MIRROR=http://ftpmaster.internal/ubuntu/ ;;
-	*)			;;
-esac
+if [ -z "$MIRROR" ]; then
+	case $(hostname --fqdn) in
+		bld-*.mmjgroup.com)	;;
+		*.mmjgroup.com)
+			case $ARCH in
+				i386|amd64)	MIRROR=http://archive.mmjgroup.com/ubuntu/ ;;
+				*)		MIRROR=http://archive.mmjgroup.com/ubuntu-ports/ ;;
+			esac
+			;;
+		*.0c3.net)		MIRROR=http://ftp.iinet.net.au/linux/ubuntu/ ;;
+		*.ubuntu.com)		MIRROR=http://ftpmaster.internal/ubuntu/ ;;
+		*.warthogs.hbd.com)	MIRROR=http://ftpmaster.internal/ubuntu/ ;;
+		*.buildd)		MIRROR=http://ftpmaster.internal/ubuntu/ ;;
+	esac
+fi
 
 mkdir -p config/chroot_local-tasklists config/chroot_local-packagelists
 rm -f config/chroot_local-tasklists/livecd-rootfs.list config/chroot_local-packagelists/livecd-rootfs.list