Add tests for operator<<(ostream, Indexer)
Add tests for operator<<(ostream, Indexer)

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