lots of cleanup

so fast interrupts overflow the kernel stack
fix: cli() before lapic_eoi()

nesting cli/sti: release shouldn't always enable interrupts
separate setup of lapic from starting of other cpus, so cpu() works earlier
flag to disable locking in console output
make locks work even when curproc==0
(still crashes in clock interrupt)

succeeds at usertests.c pipe test

usertest.c tests pre-emption
kill()

swtch idles on per-CPU stack, not on calling process's stack
fix pipe bugs
usertest.c tests pipes, fork, exit, close