A patch for /sys/src/cmd/cpu.c

This patch is designed to be upper compatible to current cpu.c

1. execution local binary
cpu -c localcommand
exits.

now perm bit of /dev/cpunote is 664
writing some message to /dev/cpunote will terminate exportfs
(we should restrict the message such as "finished", but I am lazy)


2. grid capable
now "user" is taken from /dev/user
and the user's home and profile is assigned as follows:
(using rc notation)

if (! test -e /usr/$user)
	home=/usr/none
if (! test -e $home/lib/profile)
	bind /usr/none $home

thus grid user will execute /usr/none/lib/profile

3. added some log information

4. tiny bug fix for usage message
-p to -P