address comments
address comments

* add TODO for Scalar Array Kernel use.

chainer/chainer,hvy/chainer,okuta/chainer,chainer/chainer,chainer/chainer,okuta/chainer,wkentaro/chainer,hvy/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,niboshi/chainer,okuta/chainer,chainer/chainer,wkentaro/chainer,okuta/chainer,hvy/chainer,wkentaro/chainer,hvy/chainer,pfnet/chainer,niboshi/chainer,niboshi/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,wkentaro/chainer,niboshi/chainer,tkerola/chainer