Made the default buttons on the dialog active and focused upon the
dialog appearence.
Bound 'Escape' and 'Return' keys to the dialog dismissal where it
was appropriate: mainly for dialogs with only one button and no
editable fields.
Unified the look of the "About gitk" and "Key bindings" dialogs.
Signed-off-by: Eygene Ryabinkin <rea-git@codelabs.ru>
Signed-off-by: Paul Mackerras <paulus@samba.org>