Mangle /etc/backup.d permissions at build time rather than at postinst time.

debian/backupninja.postinst

 #!/bin/sh
 set -e
 
-# Automatically added by dh_installmenu
-if [ "$1" = "configure" ] 
-then
-        chmod 770 /etc/backup.d
-fi
-
 # dh_installdeb will replace this with shell code automatically
 # generated by other debhelper scripts.
 

debian/rules

@@ -21,6 +21,10 @@ override_dh_auto_install:
 override_dh_compress:
 	dh_compress -Xexample
 
+override_dh_fixperms:
+	dh_fixperms
+	chmod 770 $(TMP)/etc/backup.d
+
 override_dh_installchangelogs:
 	dh_installchangelogs ChangeLog