add wrapper for new functions due to compability on older wp

semmelstatzR_startup.php

@@ -84,4 +84,11 @@ if(class_exists("Upgrademe")) {
         return 'http://www.php-backoffice.de/updates/test/semr_update.php';
     }
 }
-?>
+
+// function wrappers for older wp versions
+if(!function_exists("plugin_dir_path")) {
+    function plugin_dir_path($file) {
+        return trailingslashit(dirname($file));
+    }
+}
+?>