lowercase: LATIN SMALL LETTER SHARP S (U+00DF)
uppercase: LATIN CAPITAL LETTER SHARP S (U+1E9E)

The uppercase sharp s (XK_ssharp) is a relatively recent addition to unicode
but was added to the relevant keyboard layouts in xkeyboard-config-2.25
(d1411e5e95c)
xkeyboard-config/xkeyboard-config#144

Alas, the CapsLock behavior was broken on the finnish layout (maybe others).
This was due to xkbcomp using XConvertCase() to determine whether a key
requires the type FOUR_LEVEL_ALPHABETIC or FOUR_LEVEL_SEMIALPHABETIC.

Let's make this function return the right lower/upper symbols for the sharp s
and hope that the world won't get any worse because of it.

#110



Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>