Fix rpow bug
Fix rpow bug

sinhrks/chainer,okuta/chainer,hvy/chainer,laysakura/chainer,jfsantos/chainer,niboshi/chainer,hidenori-t/chainer,woodshop/chainer,wkentaro/chainer,keisuke-umezawa/chainer,cupy/cupy,jnishi/chainer,masia02/chainer,delta2323/chainer,niboshi/chainer,tigerneil/chainer,t-abe/chainer,tereka114/chainer,ktnyt/chainer,tkerola/chainer,sinhrks/chainer,hvy/chainer,kashif/chainer,benob/chainer,ktnyt/chainer,wkentaro/chainer,wkentaro/chainer,chainer/chainer,kiyukuta/chainer,sou81821/chainer,Kaisuke5/chainer,wkentaro/chainer,cupy/cupy,cupy/cupy,hvy/chainer,1986ks/chainer,niboshi/chainer,muupan/chainer,minhpqn/chainer,bayerj/chainer,yanweifu/chainer,ktnyt/chainer,rezoo/chainer,kuwa32/chainer,ytoyama/yans_chainer_hackathon,okuta/chainer,ronekko/chainer,jnishi/chainer,umitanuki/chainer,okuta/chainer,aonotas/chainer,chainer/chainer,t-abe/chainer,kikusu/chainer,truongdq/chainer,woodshop/complex-chainer,okuta/chainer,ikasumi/chainer,AlpacaDB/chainer,chainer/chainer,jnishi/chainer,muupan/chainer,ktnyt/chainer,chainer/chainer,keisuke-umezawa/chainer,elviswf/chainer,jnishi/chainer,cupy/cupy,AlpacaDB/chainer,tscohen/chainer,wavelets/chainer,ysekky/chainer,hvy/chainer,keisuke-umezawa/chainer,benob/chainer,truongdq/chainer,pfnet/chainer,kikusu/chainer,niboshi/chainer,anaruse/chainer,cemoody/chainer,keisuke-umezawa/chainer