use numpy.issubdtype to support numpy.scalar in roi_average_pooling_2d.py
use numpy.issubdtype to support numpy.scalar in roi_average_pooling_2d.py

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