Bug report

Bug summary
Running arbitrary tests with matplotlib-2.0.1 results in
AttributeError: 'QPixmap' object has no attribute 'setDevicePixelRatio'

matplotlib-2.0.0 works fine

Arbitrary test, f.i.
python histogram_demo_cumulative.py

**Actual outcome**

<!--The output produced by the above code, which may be a screenshot, console output, etc.-->

If applicable, paste the console output here

`Traceback (most recent call last):
File "histogram_demo_cumulative.py", line 16, in
histtype='step', cumulative=True)
File "/usr/local/lib/python2.7/site-packages/matplotlib-2.0.1-py2.7-linux-x86_64.egg/matplotlib/pyplot.py", line 3066, in hist
ax = gca()
File "/usr/local/lib/python2.7/site-packages/matplotlib-2.0.1-py2.7-linux-x86_64.egg/matplotlib/pyplot.py", line 950, in gca
return gcf().gca(**kwargs)
File "/usr/local/lib/python2.7/site-packages/matplotlib-2.0.1-py2.7-linux-x86_64.egg/matplotlib/pyplot.py", line 586, in gcf
return figure()
File "/usr/local/lib/python2.7/site-packages/matplotlib-2.0.1-py2.7-linux-x86_64.egg/matplotlib/pyplot.py", line 535, in figure
**kwargs)
File "/usr/local/lib/python2.7/site-packages/matplotlib-2.0.1-py2.7-linux-x86_64.egg/matplotlib/backends/backend_qt4agg.py", line 46, in new_figure_manager
return new_figure_manager_given_figure(num, thisFig)
File "/usr/local/lib/python2.7/site-packages/matplotlib-2.0.1-py2.7-linux-x86_64.egg/matplotlib/backends/backend_qt4agg.py", line 54, in new_figure_manager_given_figure
return FigureManagerQT(canvas, num)
File "/usr/local/lib/python2.7/site-packages/matplotlib-2.0.1-py2.7-linux-x86_64.egg/matplotlib/backends/backend_qt5.py", line 488, in init
self.toolbar = self._get_toolbar(self.canvas, self.window)
File "/usr/local/lib/python2.7/site-packages/matplotlib-2.0.1-py2.7-linux-x86_64.egg/matplotlib/backends/backend_qt5.py", line 539, in _get_toolbar
toolbar = NavigationToolbar2QT(canvas, parent, False)
File "/usr/local/lib/python2.7/site-packages/matplotlib-2.0.1-py2.7-linux-x86_64.egg/matplotlib/backends/backend_qt5.py", line 585, in init
NavigationToolbar2.init(self, canvas)
File "/usr/local/lib/python2.7/site-packages/matplotlib-2.0.1-py2.7-linux-x86_64.egg/matplotlib/backend_bases.py", line 2760, in init
self._init_toolbar()
File "/usr/local/lib/python2.7/site-packages/matplotlib-2.0.1-py2.7-linux-x86_64.egg/matplotlib/backends/backend_qt5.py", line 601, in _init_toolbar
a = self.addAction(self._icon(image_file + '.png'),
File "/usr/local/lib/python2.7/site-packages/matplotlib-2.0.1-py2.7-linux-x86_64.egg/matplotlib/backends/backend_qt5.py", line 591, in _icon
pm.setDevicePixelRatio(self.canvas._dpi_ratio)
AttributeError: 'QPixmap' object has no attribute 'setDevicePixelRatio'

Expected outcome

Matplotlib version

• Operating System: Linux
• Matplotlib Version: 2.0.1
• Python Version: 2.7.13
• Jupyter Version (if applicable):
• Other Libraries:

Installed from source