Move common code out of {ols,wls}_fit_tensor
Move common code out of {ols,wls}_fit_tensor

JohnGriffiths/dipy,villalonreina/dipy,FrancoisRheaultUS/dipy,matthieudumont/dipy,villalonreina/dipy,nilgoyyou/dipy,StongeEtienne/dipy,nilgoyyou/dipy,StongeEtienne/dipy,FrancoisRheaultUS/dipy,matthieudumont/dipy,JohnGriffiths/dipy