Add Cuda support for Log1p
Add Cuda support for Log1p

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