Instruct compiler that assert(0) does not return
Add missing #includes to futex.h
Add support for a pthread-based thread pool
Use pthread pool for asynchronous system calls
Make pthread_pool.h internal
Add missing #include (glibc bug?)
Add simple interface to query current time
Added alarm interface from akaros for simulation of alarms in linux

Uses our pthread_pool to spawn new pthreads to handle the alarms and
notify us once they are done.