Make AutocompleteModel compatible with Django 1.3.

Before QueryDict.getlist() only accepted one parameter. Compare
https://docs.djangoproject.com/en/1.3/ref/request-response/#django.http.QueryDict.getlist
with
https://docs.djangoproject.com/en/1.4/ref/request-response/#django.http.QueryDict.getlist
Add AUTHORS and CHANGELOG for commit [308584aab8bb7cf4].
Merge pull request #138 from haplo/django-1.3-fixes

Make AutocompleteModel compatible with Django 1.3.