Enforce account chooser on Google App Engine

gistfile1.txt

When using the Google App Engine Users API, there is no way to enforce the account chooser for users signed in to multiple accounts. You can do so by using `users.create_login_url` and replacing the output of the function as so:

```
from google.appengine.api import users
url = users.create_login_url()
url = url.replace('/accounts/ServiceLogin', '/a/SelectSession', 1)
```

This is not guaranteed to work if the output of `users.create_login_url` changes.