Issue #1191498 by dooug, twistor: Set drupal_set_message() to not repeat 'Missing Feeds plugin...'.

feeds.module

@@ -921,10 +921,10 @@ function feeds_plugin($plugin, $id) {
   $args = array('%plugin' => $plugin, '@id' => $id);
   if (user_access('administer feeds')) {
     $args['@link'] = url('admin/structure/feeds/' . $id);
-    drupal_set_message(t('Missing Feeds plugin %plugin. See <a href="@link">@id</a>. Check whether all required libraries and modules are installed properly.', $args), 'warning');
+    drupal_set_message(t('Missing Feeds plugin %plugin. See <a href="@link">@id</a>. Check whether all required libraries and modules are installed properly.', $args), 'warning', FALSE);
   }
   else {
-    drupal_set_message(t('Missing Feeds plugin %plugin. Please contact your site administrator.', $args), 'warning');
+    drupal_set_message(t('Missing Feeds plugin %plugin. Please contact your site administrator.', $args), 'warning', FALSE);
   }
   $class = ctools_plugin_load_class('feeds', 'plugins', 'FeedsMissingPlugin', 'handler');
   return FeedsConfigurable::instance($class, $id);