Django 1.4 support

[Troyhy]

This line throws error with django 1.4
https://github.com/bradleyg/django-ajaximage/blob/master/ajaximage/fields.py#L34

This is resolved for example here: estuans@fbf9f33

by removing the 3rd parameter from call to super(AjaxImageField, self).contribute_to_class(cls, name, virtual_only)

If there is a way to do this so that it would support Django 1.4 -> 1.8 this would be nice!

[Troyhy]

Quick fix: I placed this snipped in models.py and used AjaxImageField in my models

from ajaximage.fields import AjaxImageField as BrokenAjaxImageField
#quick fix for ajax image field Only needed with django 1.4
class AjaxImageField(BrokenAjaxImageField):
    def contribute_to_class(self, cls, name, virtual_only=False):
        super(BrokenAjaxImageField, self).contribute_to_class(cls, name)
        setattr(cls, self.name, self.descriptor_class(self))