Fixed `defined?` against protected method call

Protected methods are restricted to be called according to the
class/module in where it is defined, not the actual receiver's
class.  [Bug #16931]

test/ruby/test_defined.rb

@@ -59,6 +59,7 @@ def test_defined_protected_method
     f = Foo.new
     assert_nil(defined?(f.foo))         # protected method
     f.bar(f) { |v| assert(v) }
+    f.bar(Class.new(Foo).new) { |v| assert(v, "inherited protected method") }
   end
 
   def test_defined_undefined_method

vm_insnhelper.c

@@ -3603,7 +3603,7 @@ vm_defined(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, rb_num_t op_
 	      case METHOD_VISI_PRIVATE:
 		break;
 	      case METHOD_VISI_PROTECTED:
-		if (!rb_obj_is_kind_of(GET_SELF(), rb_class_real(klass))) {
+		if (!rb_obj_is_kind_of(GET_SELF(), rb_class_real(me->defined_class))) {
 		    break;
 		}
 	      case METHOD_VISI_PUBLIC: