Fix inline template Django 1.6b4 compatibility issue

[nliberg]

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: django-admin-bootstrapped/django-admin-bootstrapped#58

[nliberg]

I actually used an OR condition at first, but then changed it into two separate lines before I committed since that's how it was done in the bootstrapped commit (that commit differs from the linked discussion in this regard). Now I have joined the two if lines into one.

I am quite new to Github and a bit uncertain of what is considered best practices regarding revising pull requests (whether one is to add commits, or rewrite history in order to keep the log clean). I hope you can squash the second commit when you merge.