#230 Unbound keyboard shortcut acts as if Command unpressed.

[David A. Mellis]

I'm having a problem with keyboard shortcuts involved
the Command (Apple) key on the Mac. If I use an
unbound key combination (e.g. Command-Y) in a source
editor, a "y" is inserted. To be consistent with other
Mac programs, the use of an unbound keyboard shortcut
should do nothing.

Version 0.4 of Boa Constructor with wxPython 2.5.4.1.