use staticfiles finders to find media files if STATIC_URL is defined

[derek73]

Django 1.3 introduces staticfiles to store static app-specific media files. The files can be located in various locations around your project that you can define through your STATICFILES_FINDERS and STATICFILES_DIRS settings. This change uses the staticfiles finder to find the media files.

[monokrome]

In my opinion, you shouldn't be doing this in production, because you should be using collectstatic and serving static files through your HTTP server or a static file service and not through Django itself. Not only is efficiency an issue, but this patch would only provide unneeded extra confusion to developers in debug mode - so, I believe that it is not helpful in production or debug environments.