implement CudaNdarray.copy to have the same api as ndarray.

theano/sandbox/cuda/cuda_ndarray.cu

@@ -578,6 +578,9 @@ static PyMethodDef CudaNdarray_methods[] =
     {"__deepcopy__", 
         (PyCFunction)CudaNdarray_DeepCopy, METH_O,
         "Create a copy of this object"},
+    {"copy", 
+        (PyCFunction)CudaNdarray_Copy, METH_NOARGS,
+        "Create a copy of this object"},
     {"reduce_sum",
         (PyCFunction)CudaNdarray_ReduceSum, METH_O,
         "Reduce over the given dimensions by summation"},