Fix for false "internal error" message in Browser 

Hello, 

the issue already described in https://github.com/jaredhanson/passport-google/issues/3 unfortunately occurs in vanilla openid apps too. So if I run your example and enter a wrong URL in the login field like this
![login](https://f.cloud.github.com/assets/1558052/366202/49745b46-a279-11e2-861b-9e2178e583d2.png)
I get an error stack trace displayed in the browser.
![afterLogin](https://f.cloud.github.com/assets/1558052/366206/85b2db0a-a279-11e2-9077-e68d1ad64629.png)
The reason for this behavior is that the strategy interpretes a wrong URL as internal error although it can actually be entered by a user.
After applying the suggested fix the wrong input results in a redirect back to the login page which I think is a correct behavior.
Please check this issue, it is a show stopper.

Kind regards, Dimitry