Alt and Command keys in the quartz backend

[Michael Natterer <mitch gimp org>]

Hi all,

Currently, the mapping of the Alt and Command keys on the mac
is completely screwed:

- The key labeled "Command" maps to GDK_MOD1_MASK (which is
  essentially interpreted as Alt by all existing code)

- The key labeled "Alt" isn't mapped to any modifier at all

Now there is a lot of discussion in these bug reports:

https://bugzilla.gnome.org/show_bug.cgi?id=607115
https://bugzilla.gnome.org/show_bug.cgi?id=605799

but at the bottom of all that is the above mentioned
problem. After it's fixed we can fix whatever keymap
issues in GTK on top.

It seems pretty obvious to me that the key labeled
"Alt" should produce GDK_MOD1_MASK because all existing
code considers that being the "Alt" key.

The only question is what to map "Command" to, and we
are free to choose whatever, since the behavior will
change away from the current one of producing GDK_MOD1_MASK
anyway.

I personally prefer GDK_META_MASK because it's what the
"Windows" key is mapped to on PC keyboards, but that's not
a strong reason (and it is, as saidm completely arbitrary
anyway).

Opinions? I volunteer to patch up all 3 branches once
we come to an agreement.

Regards,
--Mitch