Handle the Ctrl modifier key ourselves if necessary.

Handle the Ctrl modifier key ourselves if necessary.

The Quartz GDK back end, if you press (say) Ctrl-A, will generate a
GdkKeyEvent with keyval='a' and state=CONTROL, but it'll have a
translated string of "a" where the X back end would have returned
"\001". So we have to do our own translation, which fortunately isn't
hard.