Fix file save error on Windows

I ran the test suite on Windows 7 using the Anaconda environment and encountered an issue where I could not save `jpg` files using the `qt_plugin` in a `novice` test.  So, I replaced the `jpg`s with `png`s.  I put a debug point before `qimg.save` per [stackoverflow](http://stackoverflow.com/questions/7152597/qt-unable-to-save-jpeg-files).

```python
(Pdb) im = QtGui.QImageWrite('test.jpg')
(Pdb) im.write(qimg)
False
(Pdb) im.errorString()
PyQt4.QtCore.QString(u'Unsupported image format')
```