xserver-common: use git patches and add functions file

* otherwise we were depending on initscripts to provide it without RDEPENDing on it

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Acked-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>