make PickledObjectField work with postgresql_psycopg2 backend
make PickledObjectField work with postgresql_psycopg2 backend

peterayeni/rapidsms,lsgunth/rapidsms,caktus/rapidsms,caktus/rapidsms,dimagi/rapidsms,ehealthafrica-ci/rapidsms,peterayeni/rapidsms,caktus/rapidsms,lsgunth/rapidsms,ehealthafrica-ci/rapidsms,ken-muturi/rapidsms,catalpainternational/rapidsms,ken-muturi/rapidsms,unicefuganda/edtrac,eHealthAfrica/rapidsms,lsgunth/rapidsms,catalpainternational/rapidsms,unicefuganda/edtrac,lsgunth/rapidsms,eHealthAfrica/rapidsms,catalpainternational/rapidsms,ehealthafrica-ci/rapidsms,peterayeni/rapidsms,catalpainternational/rapidsms,dimagi/rapidsms,unicefuganda/edtrac,ken-muturi/rapidsms,peterayeni/rapidsms,eHealthAfrica/rapidsms