Fix busted xkeymap.txt creation.

Signed-off-by: Ray Lehtiniemi <rayl@mail.com>
Make a note about X11 modifiers in event structure.

To use these would require a rethink of the core code, rather
than just reusing a hacked up version of the console code.

Signed-off-by: Ray Lehtiniemi <rayl@mail.com>