cleanup empty platforms on upgrade

debian/aegir-hostmaster.postinst

@@ -53,6 +53,14 @@ case "$1" in
                 echo "upgrading the frontend from $drupal_root to $NEW_PLATFORM"
                 cd "$drupal_root"
                 su -s /bin/sh aegir -c "drush hostmaster-migrate $FLAGS '$site_uri' '$NEW_PLATFORM'"
+                cd $HOME
+                sites=`ls "$drupal_root/sites" | egrep -v '^all|default$'`
+                if [ -z "$sites" ]; then
+                    echo "backing up old platform to $HOME/backups/$drupal_root.tgz"
+                    tar -c -z -f "$HOME/backups/$drupal_root.tgz" "$drupal_root"
+                    echo "removing old platform from $HOME/$drupal_root"
+                    rm -rf "$HOME/$drupal_root"
+                fi
             fi
         else
             db_get "aegir/site"