Make tests public. Rewrite most tests. Add tests.

Major revisions to documentation and assignments.
Implement good solutions to all assignments.
Rewrite pintos script, fsutils, and Pintos command line parsing to
support put, get of multiple files.
New pintos-mkdisk script for what pintos doesn't do anymore.
Make backtrace more friendly.
Major revisions to base file system.
Get rid of names passed to synch primitives.
Break intr_register() into intr_register_ext() and intr_register_int().
Revise bitmap code.
Add console_locked_by_current_thread() and use it.
munmap() has void return value (in lib/user/syscall.c).
Update expected tools versions.
Document use of qemu.
Add realloc() function to malloc implementation.
Add is_user_vaddr() and is_kernel_vaddr(), use in mmu.h.
Add sema_try_down(), lock_try_acquire().
Add memory barrier.
Extend default time slice to 4 ticks and calculate time slices
properly (don't just switch whenever timer_ticks() % 4 == 0).
Fix writing to palloc'd memory without checking against null
in pagedir_create().
Invalidate TLB when we mark pages not accessed or not dirty.
Revise other pagedir code.
Make load() less nasty-looking.