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
enforce rule: all kernel data structures and constants
go in syscall module.
move things that should be in syscall out of net.
make net a single package.
R=r
OCL=15985
CL=15994