added unique_together constraint to persistantconnections
added unique_together constraint to persistantconnections

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