Support v2 PyQt4 APIs and PySide in kernel's GUI support.

Closes gh-8.

IPython/external/qt_for_kernel.py

@@ -0,0 +1,12 b''
+""" Import Qt in a manner suitable for an IPython kernel.
+"""
+
+import sys
+
+# Older versions of matplotlib do not support PyQt4 v2 APIs or PySide, so we
+# cannot go through the preferred mechanism.
+matplotlib = sys.modules.get('matplotlib')
+if matplotlib and matplotlib.__version__ <= '1.0.1':
+    from PyQt4 import QtCore, QtGui
+else:
+    from IPython.external.qt import QtCore, QtGui

IPython/lib/guisupport.py

@@ -109,7 +109,7 b' def start_event_loop_wx(app=None):'
 
 def get_app_qt4(*args, **kwargs):
     """Create a new qt4 app or return an existing one."""
-    from PyQt4 import QtGui
+    from IPython.external.qt_for_kernel import QtGui
     app = QtGui.QApplication.instance()
     if app is None:
         if not args:

IPython/lib/inputhook.py

@@ -181,7 +181,8 b' class InputHookManager(object):'
         But, we first check to see if an application has already been 
         created.  If so, we simply return that instance.
         """
-        from PyQt4 import QtCore
+        from IPython.external.qt_for_kernel import QtCore, QtGui
+
         # PyQt4 has had this since 4.3.1.  In version 4.2, PyOS_InputHook
         # was set when QtCore was imported, but if it ever got removed,
         # you couldn't reset it.  For earlier versions we can
@@ -190,8 +191,8 b' class InputHookManager(object):'
             QtCore.pyqtRestoreInputHook()
         except AttributeError:
             pass
+
         self._current_gui = GUI_QT4
-        from PyQt4 import QtGui
         app = QtCore.QCoreApplication.instance()
         if app is None:
             app = QtGui.QApplication([" "])

IPython/zmq/ipkernel.py

@@ -465,7 +465,7 b' class QtKernel(Kernel):'
     def start(self):
         """Start a kernel with QtPy4 event loop integration."""
 
-        from PyQt4 import QtCore
+        from IPython.external.qt_for_kernel import QtCore
         from IPython.lib.guisupport import get_app_qt4, start_event_loop_qt4
 
         self.app = get_app_qt4([" "])