Avoid copying in python bindings
Avoid copying in python bindings

niboshi/chainer,pfnet/chainer,hvy/chainer,wkentaro/chainer,hvy/chainer,chainer/chainer,wkentaro/chainer,niboshi/chainer,wkentaro/chainer,chainer/chainer,hvy/chainer,chainer/chainer,niboshi/chainer,niboshi/chainer,chainer/chainer,hvy/chainer,wkentaro/chainer