Refactor FunctionNode fallback logic
Refactor FunctionNode fallback logic

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