rtapi.h:  include stdint.h conditionally

on hardy/amd64 includes differ in a subtle way - tentative fix
rtapi.h: make inclusion condition catch hardy linux/types.h
rtapi: use __u<size> instead of uint<size>_t

see remark in rtapi.h around line 70
trying to pacify hardy builds
build: dont build xeno_math.ko unless threadstyle is xenomai-kernel