OpenID: add option to enable asking for a username to append to the trusted provider...

OpenID: add option to enable asking for a username to append to the trusted provider's base URL. Good for hooking up with sites like WikiHow, where usernames are appended to a base URL to get a profile URL which is used as the provider.

$config['openid']['append_username'] = true;
or check 'Append a username to base URL' in OpenID admin panel.