require at least libicu version 4.2 where fromUTF8 has been introduced

Signed-off-by: Sven Nierlein <Sven.Nierlein@consol.de>
only use unicode if we found libicu

older versions don't have fromUTF8

Signed-off-by: Sven Nierlein <Sven.Nierlein@consol.de>