Adding map-reduce version of Naïve Bayes, null check for Fold version
Adding map-reduce version of Naïve Bayes, null check for Fold version

leizhangcn/Prajna,jinlmsft/Prajna,TonyAbell/Prajna,TonyAbell/Prajna,YuxiaoHu/Prajna,BrunoBozza/Prajna,MSRCCS/Prajna,dVakulen/Prajna,jinlmsft/Prajna,jinlmsft/Prajna,BrunoBozza/Prajna,MSRCCS/Prajna,MSRCCS/Prajna,MSRCCS/Prajna,cloudRoutine/Prajna,leizhangcn/Prajna,hongzhili/Prajna,cloudRoutine/Prajna,BrunoBozza/Prajna,YuxiaoHu/Prajna,jinlmsft/Prajna,BrunoBozza/Prajna,dVakulen/Prajna,hongzhili/Prajna