support django versions < 1.3: check for ListView existence before declaring AlphafilterListView
support django versions < 1.3: check for ListView existence before declaring AlphafilterListView

bltravis/django-alphabetfilter,affan2/django-alphabetfilter,affan2/django-alphabetfilter,affan2/django-alphabetfilter,bltravis/django-alphabetfilter,bltravis/django-alphabetfilter