Merge BSF 1956:1958 into branch-1_7

Small improvement:
  Random selection of pictures on notifications.

Caddie:
  Fix issue when the are not pictures attached to disassociated categories


git-svn-id: http://piwigo.org/svn/branches/branch-1_7@1959 68402e56-0260-453c-a942-63ccdbb3a9ee

include/functions_notification.inc.php

@@ -478,6 +478,7 @@ SELECT DISTINCT id, path, name, tn_ext, file
   '.$where_sql.'
     AND date_available="'.$dates[$i]['date_available'].'"
     AND tn_ext IS NOT NULL
+  ORDER BY RAND(NOW())
   LIMIT 0,'.$max_elements.'
 ;';
       $dates[$i]['elements'] = array();