[lmi] F2 in wxGrid checkbox cell

[Greg Chicares]

What should happen if I press F2 when a wxGrid checkbox cell is selected?

Observed behavior: the value is toggled.

Expected behavior: I don't know. The observed behavior just seemed surprising,
because I expect F2 never to change a cell's contents. But if it doesn't
change anything, then it can only do nothing, and that's useless, although
(arguably) less surprising. I see no other sensible option: e.g., popping
up a list with "yes" and "no" choices would be ghastly.

I tried doing this in the 'libreoffice' and 'excel' spreadsheet programs,
but they seem to treat checkboxes as free-floating elements that aren't
confined to any particular cell (which of course is not what we want for lmi).

Given that established spreadsheet programs offer no guidance, I suppose
any plausible action like {toggle-checkbox, do-nothing} is okay, so I'm not
asking for any change (unless end users express some strong opinion, which
is unlikely).