ENH: Allow QVTKRenderWindowInteractor.py to be used with PySide.

Thanks to Hadrien Mary for the patch.

Change-Id: I3d945aa5e15045ae12d054f0475b54b828860c71

Wrapping/Python/vtk/qt4/QVTKRenderWindowInteractor.py

@@ -28,7 +28,13 @@ Changes by Phil Thompson, Mar. 2008
 """
 
 
-from PyQt4 import QtCore, QtGui
+try:
+    from PyQt4 import QtCore, QtGui
+except ImportError:
+    try:
+        from PySide import QtCore, QtGui
+    except ImportError as err:
+        raise ImportError("Cannot load either PyQt or PySide")
 import vtk