Fixes issue #40

You see that error because of call of `WebUser::updateSession()`, that is called from `User::afterSave()`, that is triggered in `ActivationController::actionActivation()`:
```
php
elseif(isset($find->activkey) && ($find->activkey==$activkey)) {
				$find->activkey = UserModule::encrypting(microtime());
				$find->status = 1;
				$find->save(); // <<< HERE TRIGGERED
			    $this->render('/user/message',array('title'=>UserModule::t("User activation"),'content'=>UserModule::t("You account is activated.")));
			}
```

but the problem is, that the user in this moment is not loged in! 
I am not using yii-user, but when I have all understood, that behevior can also be generated in clean yii-user extension, with `WebUser::autoLogin = false`, so I think, that the error should be fixed in yii-user in User modell.