Inconsistency: can instantiate Tensor from List, but cannot instantiate Variable

```
    V = torch.Tensor([
        [0.7, 0],
        [0.3, 0],
        [0.2, 0]
    ])
```
=> Ok

```
    V = autograd.Variable([
        [0.7, 0],
        [0.3, 0],
        [0.2, 0]
    ])
```
=> Fail