usertest for big write()s
push begin_trans/commit_trans down into syscalls

Remove device mapping from bootpgdir
Remove unnecessary vmenable
Set CPUS back to 2 in Makefile
Passes all usertests

Allocate proper kernel page table immediately in main using boot allocator
Remove pginit
Simplify address space layout a tiny bit
More to come (e.g., superpages to simplify static table)

Maybe not necessary, but don't want to waste time figuring this out again

All tests pass

Passes all tests now (but need to update usertests to allow for more than 640k)

Very important to give qemu memory through PHYSTOP :(

Passes usertests and stressfs
Seems to recover correctly in a number of simple cases

At some point between gcc 4.4 and 4.6, omitting the frame pointer
became default if any -O is specified.  getcallerpcs relies on the
frame pointer, so bring it back.

[ cherry-picked de6075ff0978108daea1d658425bcb37663a98a0 ]

Conflicts:

	fs.c

does not affect line numbers

Variable declarations at top of function,
separate from initialization.

Use == 0 instead of ! for checking pointers.

Consistent spacing around {, *, casts.

Declare 0-parameter functions as (void) not ().

Integer valued functions return -1 on failure, 0 on success.