- Some cleanup

Finally rid of the strcasestr warning

There is something seriously messed up in these files though
(like the declaration in xtag.h do not match the definition in xtag.c!)

(which includes config.h which defines the platform feature macros)
Also remember stdio, string and stdlib are included implicitly

services_discovery.c: Patch by Alexander Gall <gall # switch.ch>, avoid crashing on systems that don't handle NULL string in ..printf.