add shim for external/qt_for_kernel.py

IPython/external/qt_for_kernel.py

@@ -0,0 +1,3 b''
+# shim for code that expects this to live in external.
+# TODO: issue deprecation warning on import from here?
+from IPython.lib.qt_for_kernel import *
  No newline at end of file

IPython/lib/qt_for_kernel.py

@@ -4,13 +4,13 b' This is the import used for the `gui=qt` or `matplotlib=qt` initialization.'
 
 Import Priority:
 
-if Qt4 has been imported anywhere else:
+if Qt has been imported anywhere else:
    use that
 
 if matplotlib has been imported and doesn't support v2 (<= 1.0.1):
     use PyQt4 @v1
 
-Next, ask ETS' QT_API env variable
+Next, ask QT_API env variable
 
 if QT_API not set:
     ask matplotlib via rcParams['backend.qt4']
@@ -26,8 +26,7 b' if QT_API not set:'
         except:
             fallback on PySide
 else:
-    use PyQt @v2 or PySide, depending on QT_API
-    because ETS doesn't work with PyQt @v1.
+    use what QT_API says
 
 """
 
@@ -43,6 +42,8 b' _qt_apis = (QT_API_PYSIDE, QT_API_PYQT, QT_API_PYQT5, QT_API_PYQTv1,'
             QT_API_PYQT_DEFAULT)
 
 #Constraints placed on an imported matplotlib
+# TODO: check that this is still consistent with what matplotlib supports,
+# in particular with regard to qt5.
 def matplotlib_options(mpl):
     if mpl is None:
         return