Cleanup error messages on exit

[sapi]

When MyPyTutor is exited (using the red x), it prints an absurd amount of crap to stderr:

In [1]: %run code/MyPyTutor.py

In [2]: invalid command name "84072048timer_event"
    while executing
"84072048timer_event"
    ("after" script)
invalid command name "84012768font_timer_event"
    while executing
"84012768font_timer_event"
    ("after" script)

Do you really want to exit ([y]/n)?
Exception ignored in: <bound method MultiCall.__del__ of <idlelib.MultiCall.MultiCallCreator.<locals>.MultiCall object a
t 0x0464E050>>
Traceback (most recent call last):
  File "C:\Python34\lib\idlelib\MultiCall.py", line 413, in __del__
    self.__binders[triplet[1]].unbind(triplet, func)
  File "C:\Python34\lib\idlelib\MultiCall.py", line 102, in unbind
    self.widget.unbind(self.widgetinst, self.sequence, self.handlerid)
  File "C:\Python34\lib\tkinter\__init__.py", line 1092, in unbind
    self.tk.call('bind', self._w, sequence, '')
_tkinter.TclError: can't invoke "bind" command: application has been destroyed
Exception ignored in: <bound method _ComplexBinder.__del__ of <idlelib.MultiCall._ComplexBinder object at 0x0464E090>>
Traceback (most recent call last):
  File "C:\Python34\lib\idlelib\MultiCall.py", line 244, in __del__
    self.widget.unbind(self.widgetinst, seq, id)
  File "C:\Python34\lib\tkinter\__init__.py", line 1092, in unbind
    self.tk.call('bind', self._w, sequence, '')
_tkinter.TclError: can't invoke "bind" command: application has been destroyed
Exception ignored in: <bound method _ComplexBinder.__del__ of <idlelib.MultiCall._ComplexBinder object at 0x0464E0B0>>
Traceback (most recent call last):
  File "C:\Python34\lib\idlelib\MultiCall.py", line 244, in __del__
    self.widget.unbind(self.widgetinst, seq, id)
  File "C:\Python34\lib\tkinter\__init__.py", line 1092, in unbind
    self.tk.call('bind', self._w, sequence, '')
_tkinter.TclError: can't invoke "bind" command: application has been destroyed
Exception ignored in: <bound method _ComplexBinder.__del__ of <idlelib.MultiCall._ComplexBinder object at 0x0464E2D0>>
Traceback (most recent call last):
  File "C:\Python34\lib\idlelib\MultiCall.py", line 244, in __del__
    self.widget.unbind(self.widgetinst, seq, id)
  File "C:\Python34\lib\tkinter\__init__.py", line 1092, in unbind
    self.tk.call('bind', self._w, sequence, '')
_tkinter.TclError: can't invoke "bind" command: application has been destroyed
Exception ignored in: <bound method _ComplexBinder.__del__ of <idlelib.MultiCall._ComplexBinder object at 0x0464E4F0>>
Traceback (most recent call last):
  File "C:\Python34\lib\idlelib\MultiCall.py", line 244, in __del__
    self.widget.unbind(self.widgetinst, seq, id)
  File "C:\Python34\lib\tkinter\__init__.py", line 1092, in unbind
    self.tk.call('bind', self._w, sequence, '')
_tkinter.TclError: can't invoke "bind" command: application has been destroyed
Exception ignored in: <bound method _SimpleBinder.__del__ of <idlelib.MultiCall._SimpleBinder object at 0x0464EA30>>
Traceback (most recent call last):
  File "C:\Python34\lib\idlelib\MultiCall.py", line 109, in __del__
    self.handlerid)
  File "C:\Python34\lib\tkinter\__init__.py", line 1092, in unbind
    self.tk.call('bind', self._w, sequence, '')
_tkinter.TclError: can't invoke "bind" command: application has been destroyed
Exception ignored in: <bound method _SimpleBinder.__del__ of <idlelib.MultiCall._SimpleBinder object at 0x0464EA50>>
Traceback (most recent call last):
  File "C:\Python34\lib\idlelib\MultiCall.py", line 109, in __del__
    self.handlerid)
  File "C:\Python34\lib\tkinter\__init__.py", line 1092, in unbind
    self.tk.call('bind', self._w, sequence, '')
_tkinter.TclError: can't invoke "bind" command: application has been destroyed

This should probably be cleaned up so as to avoid scaring the students.