also call after_any_fetch after user is set -> after_change_user

[grosser]

I missed the point that users can also be just set in my first pull,
so I renamed the hook to reflect that its called after user was changed,
and added the callback to set_user and user + made sure it is not called twice

(our app has to change locale whenever user is changed)

[josevalim]

I am fine with this change but @grosser wouldn't be better to simply have a callback for whenever fetch fails? We already have one for whenever fetch succeeds, so instead of having another callback overlapping, couldn't we simply have the counterpart?

[grosser]

I think that's a good idea, the combination will capture everything,
how about after_fetch_fail ?

[josevalim]

Sounds great. Can we close this then and expect a new PR from you? :) Thanks.