Make sure we register extensions only once. Removed unused member variable.

src/api.h

Index: src/api.h
diff --git a/src/api.h b/src/api.h
index 686abf75c4af0e2108da34f28a48987e5f510eec..12d6e3d08229343644b3f571933c15543b90c19b 100644
--- a/src/api.h
+++ b/src/api.h
@@ -149,12 +149,10 @@ class RegisteredExtension {
   static void UnregisterAll();
   Extension* extension() { return extension_; }
   RegisteredExtension* next() { return next_; }
-  RegisteredExtension* next_auto() { return next_auto_; }
   static RegisteredExtension* first_extension() { return first_extension_; }
  private:
   Extension* extension_;
   RegisteredExtension* next_;
-  RegisteredExtension* next_auto_;
   static RegisteredExtension* first_extension_;
 };