moved all ProductModel safty checks into own method
moved all ProductModel safty checks into own method

jrief/django-shop,khchine5/django-shop,rfleschenberg/django-shop,rfleschenberg/django-shop,khchine5/django-shop,awesto/django-shop,nimbis/django-shop,jrief/django-shop,khchine5/django-shop,awesto/django-shop,nimbis/django-shop,jrief/django-shop,awesto/django-shop,khchine5/django-shop,divio/django-shop,rfleschenberg/django-shop,rfleschenberg/django-shop,nimbis/django-shop,divio/django-shop,nimbis/django-shop,jrief/django-shop,divio/django-shop