Change dev read/write functions
to take inode* instead of minor number.

Unlock console inode during console_read
and console_write.  Otherwise background
processes cannot write to console while the
shell is reading it waiting for input.

if no lapic available, use 8253pit for clock
now xv6 runs both on qemu (uniprocessor) and bochs (uniprocessor and MP)

xv6 seems to work fine on uniprocessor now.

don't use the same name for two different pieces of code

delete unused functions
a few comments

better parsing of sh commands (copied from jos sh)
cat: read from 1 if no args
sbrk system call, but untested
getpid system call
moved locks in keyboard intr, but why do we get intr w. null characters from keyboard?

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

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