enable graceful restart of kernels in notebook

IPython/frontend/html/notebook/kernelmanager.py

@@ -43,7 +43,7 b' class MultiKernelManager(LoggingConfigurable):'
     """A class for managing multiple kernels."""
     
     kernel_manager_class = DottedObjectName(
-        "IPython.zmq.kernelmanager.KernelManager", config=True,
+        "IPython.zmq.blockingkernelmanager.BlockingKernelManager", config=True,
         help="""The kernel manager class.  This is configurable to allow
         subclassing of the KernelManager for customized behavior.
         """
@@ -87,6 +87,8 b' class MultiKernelManager(LoggingConfigurable):'
                     config=self.config,
         )
         km.start_kernel(**kwargs)
+        # start the shell channel, needed for graceful restart
+        km.start_channels(shell=True, sub=False, stdin=False, hb=False)
         self._kernels[kernel_id] = km
         return kernel_id
 
@@ -284,7 +286,7 b' class MappingKernelManager(MultiKernelManager):'
         """Restart a kernel while keeping clients connected."""
         self._check_kernel_id(kernel_id)
         km = self.get_kernel(kernel_id)
-        km.restart_kernel(now=True)
+        km.restart_kernel()
         self.log.info("Kernel restarted: %s" % kernel_id)
         return kernel_id