title: comparing torch.nn.CrossEntropyLoss with label as int and prob tensor produces an error
body: <p>I have this criterion:</p>
  <pre><code>criterion = nn.CrossEntropyLoss()
  </code></pre>
  <p>And during training phase i have:</p>
  <pre><code>label = tensor([0.])
  outputs = tensor([[0.0035, 0.0468]], grad_fn=&lt;AddmmBackward&gt;)
  </code></pre>
  <p>When i try to compare them:</p>
  <pre><code> criterion(outputs, label)
  </code></pre>
  <p>I get this error:</p>
  <pre><code>    ret = torch._C._nn.nll_loss(input, target, weight, _Reduction.get_enum(reduction), ignore_index)
  RuntimeError: Expected object of scalar type Long but got scalar type Float for argument #2 'target' in call to _thnn_nll_loss_forward
  </code></pre>