Add missing files

debian/postinst

@@ -0,0 +1,11 @@
+#!/bin/sh -e
+
+set -e
+
+if [ "$1" = configure ]; then
+  update-alternatives --install /etc/lxdm/default.conf \
+    lxdm.conf /etc/xdg/lubuntu/lxdm/lxdm.conf 60 
+fi
+
+#DEBHELPER#
+exit 0

debian/prerm

@@ -0,0 +1,10 @@
+#!/bin/sh -e
+
+set -e
+
+if [ "$1" = "remove" ] || [ "$1" = upgrade ]; then
+  update-alternatives --remove lxdm.conf /etc/xdg/lubuntu/lxdm/lxdm.conf 
+fi
+
+#DEBHELPER#
+exit 0