fixed tests and changed flext tvis aff to get dimension from trackvis header
fixed tests and changed flext tvis aff to get dimension from trackvis header

nilgoyyou/dipy,matthieudumont/dipy,nilgoyyou/dipy,FrancoisRheaultUS/dipy,matthieudumont/dipy,villalonreina/dipy,FrancoisRheaultUS/dipy,villalonreina/dipy