Fix bug.
Merge branch 'master' of https://github.com/JLangowitz/pintos

Conflicts:
	src/threads/thread.c
Merge branch 'master' of https://github.com/JLangowitz/pintos
Add increasing recent_cpu.
Fix bug on timer_interrupt() and merge.
Merge branch 'master' of https://github.com/JLangowitz/pintos