BUG: Scrolling pager in vsplit on Mac OSX tears.

On Mac OS X, scrolling the pager when it is split vertically causes the
help text to tear (i.e. the help text is unreadable).  This hack
attempts to make it a little better although the solution may not be
optimal at all.

Closes  #1150, rebased to prevent recursive merge.

IPython/frontend/qt/console/console_widget.py

@@ -364,6 +364,14 b' class ConsoleWidget(LoggingConfigurable, QtGui.QWidget):'
             QtGui.qApp.sendEvent(obj, QtGui.QDragLeaveEvent())
             return True
 
+        # Handle scrolling of the vsplit pager. This hack attempts to solve the
+        # problem of tearing of the pager window's help text on Mac OS X.  This
+        # happens with PySide and PyQt. This fix isn't perfect but makes the
+        # pager more usable.
+        elif etype in [QtCore.QEvent.Wheel, QtCore.QEvent.NativeGesture] and \
+                obj == self._page_control:
+            self._page_control.repaint()
+            return True
         return super(ConsoleWidget, self).eventFilter(obj, event)
 
     #---------------------------------------------------------------------------
@@ -965,6 +973,8 b' class ConsoleWidget(LoggingConfigurable, QtGui.QWidget):'
         elif self.kind == 'rich':
             control = QtGui.QTextEdit()
         control.installEventFilter(self)
+        viewport = control.viewport()
+        viewport.installEventFilter(self)
         control.setReadOnly(True)
         control.setUndoRedoEnabled(False)
         control.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOn)