use correct transition in screen_manager.switch_to if user passes opt…

…ion like it's described in the docs

kivy/uix/screenmanager.py

@@ -925,6 +925,7 @@ def switch_to(self, screen, **options):
             raise ScreenManagerException(
                     'ScreenManager accepts only Screen widget.')
 
+
         # stop any transition that might be happening already
         self.transition.stop()
 
@@ -933,6 +934,12 @@ def switch_to(self, screen, **options):
             if self.has_screen(screen.name):
                 screen.name = self._generate_screen_name()
 
+        # change the transition if given explicitly
+        old_transition = self.transition
+        specified_transition = options.pop("transition", None)
+        if specified_transition:
+            self.transition = specified_transition
+
         # change the transition options
         for key, value in iteritems(options):
             setattr(self.transition, key, value)
@@ -947,6 +954,7 @@ def switch_to(self, screen, **options):
         def remove_old_screen(transition):
             if old_current in self.children:
                 self.remove_widget(old_current)
+                self.transition = old_transition
             transition.unbind(on_complete=remove_old_screen)
         self.transition.bind(on_complete=remove_old_screen)