Support excluded and included mode for average pooling.
Created by: qingqing01
- cuDNN support excluded and included mode when computing the average in pool2d_avg_op.
- Caffe only supports included mode. - Caffe2 only supports excluded mode. https://github.com/pytorch/pytorch/blob/master/caffe2/operators/pool_op.cu
- Onnx only supports excluded mode. https://github.com/onnx/onnx/blob/master/docs/Operators.md#averagepool
- PyTorch supports both mode. http://pytorch.org/docs/master/nn.html#torch.nn.AvgPool2d
- Fluid only supports excluded mode now.
But some model converted from Caffe needs to use included mode in pool2d_avg_op. So add included mode supporting in Fluid.