keysym-utf: also translate special keysyms like Tab and Return

keysym-utf: also translate special keysyms like Tab and Return

The keysym2ucs.c file apparently leaves out some keysyms, which libX11
deals with separately (like in _XkbHandleSpecialSym()).
The problematic keysyms are the keypad ones (for which we already added
some support) and keysyms which use 0xff** instead of 0x00** < 0x20.
This code should fix them properly, as much as I could gather from
libX11 and http://www.cl.cam.ac.uk/~mgk25/ucs/keysym2ucs.c and other
sources (which are not aware of locale).

https://bugs.freedesktop.org/show_bug.cgi?id=56780

Reported-by: Gatis Paeglis <gatis.paeglis@digia.com>
Signed-off-by: Ran Benita <ran234@gmail.com>