use += to include rdiff-backup etc.

software/maarch/software.cfg

@@ -3,7 +3,8 @@
 extends =
   ../../stack/lapp/buildout.cfg
 
-parts =
+# += since we need rdiff-backup and friends
+parts +=
   slapos-cookbook
   apache-php-postgres
   pear-modules
@@ -11,7 +12,6 @@ parts =
   instance
   instance-apache-php
 
-
 #----------------
 #--
 #-- Main application part