Add error message for PyPy/pyqt combination

Author: mwcraig

vpython/no_notebook.py

@@ -240,6 +240,12 @@ def onClose(self, wasClean, code, reason):
     pass
 
 
+if platform.python_implementation() == 'PyPy' and _browsertype == 'pyqt':
+    raise RuntimeError('The pyqt browser cannot be used PyPy. Please use '
+                       'the default browser instead by removing '
+                       'set_browser("pyqt") from your code.')
+
+
 def start_Qapp(port):
     # creates a python browser with PyQt5
     # runs qtbrowser.py in a separate process