re-raise KeyboardInterrupt in raw_input

shortens traceback when KeyboardInterrupt is caught deep within zmq.

closes  #3786

IPython/kernel/zmq/ipkernel.py

@@ -766,6 +766,9 b' class Kernel(Configurable):'
                 ident, reply = self.session.recv(self.stdin_socket, 0)
             except Exception:
                 self.log.warn("Invalid Message:", exc_info=True)
+            except KeyboardInterrupt:
+                # re-raise KeyboardInterrupt, to truncate traceback
+                raise KeyboardInterrupt
             else:
                 break
         try: