Allow scalar `condition`
Allow scalar `condition`

including `bool` of Python

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