Add utility routines bzero, readsb so that balloc, bfree fit on one page.
Make balloc loop clearer.

Rename B_WRITE to B_DIRTY and then let ide.c
maintain the B_VALID and B_DIRTY flags.

Remove type arg to mknod (assume T_DEV).

Allow multiple arguments to ls.

nits in comments

Move initialization of %sp after
protected mode jump and change to %esp.

test files with holes (not ok)