change meaning of $GOMAXPROCS to number of cpus to use,

change meaning of $GOMAXPROCS to number of cpus to use,
not number of threads.  can still starve all the other threads,
but only by looping, not by waiting in a system call.

fix darwin syscall.Syscall6 bug.

fix chanclient bug.

delete $GOMAXPROCS from network tests.

add stripped down printf, sys.printhex to runtime.

R=r
DELTA=355  (217 added, 36 deleted, 102 changed)
OCL=20017
CL=20019