Use the soon-to-exist ubuntu-rtm archive for ubuntu-touch builds if

SUBPROJECT is ubuntu-rtm (or ubuntu-rtm/dogfood for the dogfood
version).

debian/changelog

@@ -1,3 +1,11 @@
+livecd-rootfs (2.225) UNRELEASED; urgency=medium
+
+  * Use the soon-to-exist ubuntu-rtm archive for ubuntu-touch builds if
+    SUBPROJECT is ubuntu-rtm (or ubuntu-rtm/dogfood for the dogfood
+    version).
+
+ -- Colin Watson <cjwatson@ubuntu.com>  Thu, 17 Jul 2014 12:48:17 +0100
+
 livecd-rootfs (2.224) utopic; urgency=medium
 
   * drop extra space in DEFGROUPS variable

live-build/auto/config

@@ -336,6 +336,19 @@ case $PROJECT in
 		OPTS="${OPTS:+$OPTS }--compression gzip"
 		OPTS="${OPTS:+$OPTS }--system normal"
 		OPTS="${OPTS:+$OPTS }--zsync false"
+
+		# TODO cjwatson 2014-07-17: This is a bit of an abuse of
+		# SUBPROJECT, but it's a handy thing that launchpad-buildd
+		# already passes through to us that we weren't otherwise
+		# using here.
+		case $SUBPROJECT in
+		    ubuntu-rtm/dogfood)
+			MIRROR=http://derived-archive.dogfood.content.paddev.net/ubuntu-rtm/
+			;;
+		    ubuntu-rtm)
+			MIRROR=http://derived.archive.canonical.com/ubuntu-rtm/
+			;;
+		esac
 		;;
 
 	*)