litte performance improvement

src/Storm/Model/Abstract.php

@@ -906,6 +906,11 @@ abstract class Storm_Model_Abstract {
   }
 
 
+  public function getId() {
+    return $this->_attributes['id'];
+  }
+
+
   /**
    * Return the value of attribute $field. If cannot find it, raise Exception.
    * @param string $field