Let the auto pylab backend detection work.

The kernel knows how to find the user's backend choice, so if no
backend is explicitly given, read it from the matplotlibrc file.

IPython/frontend/qt/console/ipythonqt.py

@@ -113,10 +113,7 b' def main():'
             if args.rich:
                 kernel_manager.start_kernel(pylab='payload-svg')
             else:
-                if args.pylab == 'auto':
-                    kernel_manager.start_kernel(pylab='qt4')
-                else:
-                    kernel_manager.start_kernel(pylab=args.pylab)
+                kernel_manager.start_kernel(pylab=args.pylab)
         else:
             kernel_manager.start_kernel()
     kernel_manager.start_channels()