support %matplotlib nbagg

we don't need to do anything, just add keys to a couple of dictionaries

IPython/core/pylabtools.py

@@ -21,6 +21,7 b" backends = {'tk': 'TkAgg',"
             'qt4': 'Qt4Agg',
             'qt5': 'Qt5Agg',
             'osx': 'MacOSX',
+            'nbagg': 'nbAgg',
             'inline' : 'module://IPython.kernel.zmq.pylab.backend_inline'}
 
 # We also need a reverse backends2guis mapping that will properly choose which

IPython/kernel/zmq/eventloops.py

@@ -39,6 +39,7 b' def _notify_stream_qt(kernel, stream):'
 # mapping of keys to loop functions
 loop_map = {
     'inline': None,
+    'nbagg': None,
     None : None,
 }