(backport) Fixes #11088: IDLE crashes when using F5 to run a script on OSX with Tk 8.5

(backport) Fixes #11088: IDLE crashes when using F5 to run a script on OSX with Tk 8.5
Without this patch IDLE will crash reliably on OSX when Tkinter
is linked to TkCocoa 8.5.x.

To reproduce:

* Create a new file (script.py) with the following two lines:

x = raw_input('prompt: ')
print x

* Save the script

* Run the script using the F5 keyboard shortcut
  (running from the menu works fine)

The patch is a fairly crude hack, but we haven't found a better
workaround for this Tk bug yet.