renumber system calls (run gmake clean!)
skeleton for dup system call

cd in shell
nits in mkdir, ls, etc.

stat

no more cons_put system calls
usertests tests two processes writing files

primitive ls

sh accepts 0-argument commands (like userfs)
reads from console

convert userfs to use printf
bfree
ifree
writei
start on unlink

give cpu1 a TSS and gdt for when it enters scheduler()
and a pseudo proc[] entry for each cpu
cpu0 waits for each other cpu to start up
read() for files

Add user.h for prototypes.
Add cons_puts for cleaner output.