Explicitly close prompt_toolkit event loop after running

This is recommended, see jonathanslenders/python-prompt-toolkit#287.
Normally it won't matter, because we close it just before the process
exits, but if someone is embedding it repeatedly it could leave pipes
lingering.

IPython/terminal/ptshell.py

@@ -251,8 +251,8 b' class TerminalInteractiveShell(InteractiveShell):'
                             mouse_support=self.mouse_support,
                             **self._layout_options()
         )
-        self.pt_cli = CommandLineInterface(self._app,
-                           eventloop=create_eventloop(self.inputhook))
+        self._eventloop = create_eventloop(self.inputhook)
+        self.pt_cli = CommandLineInterface(self._app, eventloop=self._eventloop)
 
     def _make_style_from_name(self, name):
         """
@@ -383,6 +383,8 b' class TerminalInteractiveShell(InteractiveShell):'
             except KeyboardInterrupt:
                 print("\nKeyboardInterrupt escaped interact()\n")
 
+        self._eventloop.close()
+
     _inputhook = None
     def inputhook(self, context):
         if self._inputhook is not None: