fix cuDNN v5 cudnnSetPoolingNdDescriptor in pool grad

theano/sandbox/gpuarray/dnn_pool_grad.c

@@ -109,7 +109,12 @@ int APPLY_SPECIFIC(dnn_pool_grad)(PyGpuArrayObject *inp,
   for(int i = 0; i < ndims; i++) {
      s[i] = *((npy_intp*)PyArray_GETPTR1(stride, i));
   }
+
+#if CUDNN_VERSION >= 5000
+  err = cudnnSetPoolingNdDescriptor(APPLY_SPECIFIC(pool), MODE_FLAG, CUDNN_PROPAGATE_NAN, ndims, w, p, s);
+#else
   err = cudnnSetPoolingNdDescriptor(APPLY_SPECIFIC(pool), MODE_FLAG, ndims, w, p, s);
+#endif
 
   if (err != CUDNN_STATUS_SUCCESS) {
     PyErr_Format(PyExc_RuntimeError, "could not set op descriptor %s", cudnnGetErrorString(err));