fix on 4.2.2 with django 1.7 : is_hidden = True
fix on 4.2.2 with django 1.7 : is_hidden = True

with django 1.7, is hidden in no loger an attribute
but a property which compare input_type with "hidden"
this commit make sur that is_hidden will always be False

can be merged in 4.2.2

strongriley/django-select2,dantagg/django-select2,SmithsonianEnterprises/django-select2,SmithsonianEnterprises/django-select2,rizumu/django-select2,hisie/django-select2,emorozov/django-select2,pbs/django-select2,applegrew/django-select2,dulaccc/django-select2,DMOJ/django-select2,rizumu/django-select2,emorozov/django-select2,patgmiller/django-select2,dulaccc/django-select2,applegrew/django-select2,dulaccc/django-select2,rizumu/django-select2,hisie/django-select2,pbs/django-select2,applegrew/django-select2,SmithsonianEnterprises/django-select2,anneFly/django-select2,anneFly/django-select2,patgmiller/django-select2,bubenkoff/django-select2,dantagg/django-select2,DMOJ/django-select2,pbs/django-select2,hobarrera/django-select2,strongriley/django-select2,anneFly/django-select2,DMOJ/django-select2,bubenkoff/django-select2,dantagg/django-select2,emorozov/django-select2,hisie/django-select2,strongriley/django-select2,hobarrera/django-select2,hobarrera/django-select2,bubenkoff/django-select2,patgmiller/django-select2