Fix inline template Django 1.6b4 compatibility issue

In the Django 1.6 beta, in `django.contrib.admin.helpers.InlineAdminForm` the function `has_auto_field` has been renamed to `needs_explicit_pk_field`. This causes the `TabularInline` and `StackedInline` to render incorrectly leading to a KeyDictError when saving records.

The error can be fixed by replacing `has_auto_field` with `needs_explicit_pk_field` in the templates: `templates/admin/edit_inline/stacked.html` and `templates/admin/edit_inline/tabular.html`
 
My modification is based on a solution by rhunwicks. For comparison see: https://github.com/riccardo-forina/django-admin-bootstrapped/issues/58