Use identity::set_active_user() instead of auth::login() when we

change providers otherwise the user_installer code is going to be
calling auth::login() which causes all kinds of unexpected weirdness,
like it triggers the handler in gallery_event which detects graphics
toolkits, and that's only supposed to run on the first admin login.

modules/gallery/libraries/IdentityProvider.php

@@ -83,7 +83,7 @@ static function change_provider($new_provider) {
 
       module::event("identity_provider_changed", $current_provider, $new_provider);
 
-      auth::login($provider->admin_user());
+      identity::set_active_user($provider->admin_user());
       Session::instance()->regenerate();
     } catch (Exception $e) {
       static $restore_already_running;