remove a couple hundred sys/param.h includes in userland code, and
also whack some sys/cdefs.h early includes which is such a brutally
bad pattern
ok bluhm mbuhl

improve clock_gettime regress:

* fix compilation error due to missing cast
* do not run sysctl during make clean and the other common regress cleanup
targets
* make it work using a separate object

improve clock_gettime regress:

* fix compilation error due to missing cast
* do not run sysctl during make clean and the other common regress cleanup
targets
* make it work using a separate object directory

show more ...

new regress: clock_gettime(2); test if CLOCK_MONOTONIC is really monotonic

suggested by kettenis@, tweaked by anton@.

ok mpi@ jca@