Monkey patch s3boto storage to properly quote file names.

This is a temporary solution until:
* django-storages issue #172 is fixed (http://code.larlet.fr/django-storages/issue/172/storageurl-should-quote-file-names-before#comment-4149177)
OR
* pull req #70 is merged (http://code.larlet.fr/django-storages/issue/172/storageurl-should-quote-file-names-before#comment-4149177)