clarify docstring Director.get_window_size

[ccanepa]

From [email protected] on June 25, 2013 11:45:18

The docstring is fine when the user is using do_not_scale = False in director init, but unhelpful for the True case.

When not using autoscale theres a need to know the real viewport dimensions.
For that case the dostring can hint to use
director._usable_width
director._usable_height

or listen to the "on_cocos_resize" event, that will pass the same parameters

Original issue: http://code.google.com/p/los-cocos/issues/detail?id=194