fix rox synchronization bug

fix concurrency bug in timer_sleep() (push up intr_disable() block)

fixed some problems with priority donation

simplify mlfqs ready list (just one queue)

added helpful lock / interrupt macros, disable interrupts lots of places they need to be, fix thread_yield

disable interrupts around more atomic blocks

finish design doc; pretty much ready to submit

final commit before submit

added jitter bugfinder

change output file name scheme for find_bug script
better behavior for orphaned children