Removed dependency on frozenset
Removed dependency on frozenset

git-svn-id: 72004cf0fdb91158a18fb5306bfb1f89abf93d11@41 ab604574-8a94-11dd-aa62-cdabd1f4ca1e

IanLee1521/django-reversion,etianen/django-reversion,Govexec/django-reversion,Beauhurst/django-reversion,matllubos/django-reversion,unicefuganda/edtrac,blag/django-reversion,fladi/django-reversion,pydanny/django-reversion,HubSpot/django-reversion,mkebri/django-reversion,matllubos/django-reversion,ixc/django-reversion,pydanny/django-reversion,unicefuganda/edtrac,lutoma/django-reversion,blag/django-reversion,Beauhurst/django-reversion,talpor/django-reversion,adonm/django-reversion,etianen/django-reversion,mkebri/django-reversion,fladi/django-reversion,ixc/django-reversion,unicefuganda/edtrac,adonm/django-reversion,IanLee1521/django-reversion,MikeAmy/django-reversion,MikeAmy/django-reversion,lutoma/django-reversion,talpor/django-reversion,cbrepo/django-reversion,Govexec/django-reversion