Fix the bug that only the first rendered filefield gets Dropzone attached.
Fix the bug that only the first rendered filefield gets Dropzone attached.

divio/django-filer,stefanfoulis/django-filer,jakob-o/django-filer,skirsdeda/django-filer,stefanfoulis/django-filer,jakob-o/django-filer,DylannCordel/django-filer,webu/django-filer,jakob-o/django-filer,stefanfoulis/django-filer,jakob-o/django-filer,DylannCordel/django-filer,DylannCordel/django-filer,divio/django-filer,DylannCordel/django-filer,skirsdeda/django-filer,jakob-o/django-filer,DylannCordel/django-filer,stefanfoulis/django-filer,stefanfoulis/django-filer,webu/django-filer,divio/django-filer,skirsdeda/django-filer,webu/django-filer,divio/django-filer,webu/django-filer,skirsdeda/django-filer,skirsdeda/django-filer