Added special case for atomic regular expressions.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 85a812217848d5690db07c8fa56edc16379e99db..367a57e91e1889dbe953e4491aeedf5a208c2596 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2812,7 +2812,7 @@ class JSValue: public JSObject {
 // Regular expressions
 class JSRegExp: public JSObject {
  public:
-  enum Type { JSCRE, INDEX_OF };
+  enum Type { JSCRE, ATOM };
 
   inline Type type_tag();
   inline void set_type_tag(Type value);