Use queryset for completion suggestions

For each instance of the autocomplete widget the queryset passed in is
registered in the autocomplete "manager". This queryset is then used
when providing auto-complete suggestions. Previously a generic
`model.objects` queryset was used for creating the suggestions.
Merge master into leifdenby-master
pep8++
Bump to v0.94.1: handle custom model managers.
Merge @leifdenby PR in master.