Add TODO comment about dtype promotion
Add TODO comment about dtype promotion

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