Bug 663856 - Make option-foo accelerators use the right symbol

Bug 663856 - Make option-foo accelerators use the right symbol

If the keyboard group shifting modifier is *also* a normal
accelerator modifier, we need to special case it when calling
gdk_keymap_translate_keyboard_state(), so we get the right
key symbol for accelerators (for example we want Option-O,
not Option-Ø displayed in menu items). This patch should only
affect quartz where the Alt key both shifts the group and can
be used as accel modifier, and not X11 or Win32 where AltGr
is not used for accelerators.

- fix quartz' gdk_keymap_translate_keyboard_state() to return
  the right consumed_modifiers
- add _gtk_translate_keyboard_accel_state() which does the
  special casing
- use it everywhere instead of gdk_keymap_translate_keyboard_state()