fixed qtwidget.newimage to actually accept tensors.

The following fails in the current master..

```
require 'qt'
require 'qttorch'
require 'qtwidget'
require 'qtuiloader'
qim = qtwidget.newimage(image.lena())
```

Because torch.typename(image.lena()) does not equal ```'torch.Tensor'```, but whatever the default tensor type is (ie ```'torch.DoubleTensor'```).  This is fixed now.