Issue #1722180 by pcambra: Clear plugins cache on feeds_cache_clear.

feeds.module

@@ -796,6 +796,7 @@ function _feeds_importer_digest() {
 function feeds_cache_clear($rebuild_menu = TRUE) {
   cache_clear_all('_feeds_importer_digest', 'cache');
   drupal_static_reset('_feeds_importer_digest');
+  cache_clear_all('plugins:feeds:plugins', 'cache');
   ctools_include('export');
   ctools_export_load_object_reset('feeds_importer');
   drupal_static_reset('_node_types_build');