diff -r aff75b69db92 -r 2c48c091b6a2 schemas/_regproc.postgres.sql
--- a/schemas/_regproc.postgres.sql	Tue Jul 02 17:09:04 2013 +0200
+++ b/schemas/_regproc.postgres.sql	Mon Jan 13 13:47:47 2014 +0100
@@ -10,10 +10,15 @@
     SELECT array_to_string($1, ', ')
 $$ LANGUAGE SQL;;
 
+
+CREATE FUNCTION cw_array_append_unique (anyarray, anyelement) RETURNS anyarray AS $$
+    SELECT array_append($1, (SELECT $2 WHERE $2 <> ALL($1)))
+$$ LANGUAGE SQL
+
 DROP AGGREGATE IF EXISTS group_concat (anyelement) CASCADE;
 CREATE AGGREGATE group_concat (
   basetype = anyelement,
-  sfunc = array_append,
+  sfunc = cw_array_append_unique,
   stype = anyarray,
   finalfunc = comma_join,
   initcond = '{}'