Make the upload view thread safe.
Make the upload view thread safe.

This could probably be done more efficiently, but at least for now downloads won't be
mixed between threads.

brilliant-org/django-ajax-uploader,derek-adair/django-ajax-uploader,derek-adair/django-ajax-uploader,brilliant-org/django-ajax-uploader,brilliant-org/django-ajax-uploader,OnlyInAmerica/django-ajax-uploader,derek-adair/django-ajax-uploader,skoczen/django-ajax-uploader,skoczen/django-ajax-uploader,OnlyInAmerica/django-ajax-uploader