RF: Drop Python 2.6 support and stop testing on it.
RF: Drop Python 2.6 support and stop testing on it.

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