Allow plugins to be symlinks

This change makes sure that plugins can be loaded even though they are symlinks. The change makes it easier to have custom schemes to handle version control with zero-downtime deployment.

modules/system/classes/PluginManager.php

@@ -360,7 +360,9 @@ class PluginManager
             return $plugins;
         }
 
-        $it = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($dirPath));
+        $it = new RecursiveIteratorIterator(
+            new RecursiveDirectoryIterator($dirPath, RecursiveDirectoryIterator::FOLLOW_SYMLINKS)
+        );
         $it->setMaxDepth(2);
         $it->rewind();