Remove the old FIFO socket from the event queue when recreating it

The previous code had two problems:
  1) It never removed the old fd from the event loop, which meant that
if the new fd received a different index, the old fd would keeping
waking up the master process repeatedly.
  2) If the new fd got the same index but the master loop went back to
epoll_wait() fast enough, Linux would claim that the socket is ready for
reading, but read() would return 0 again, which would cause the FIFO to
be recreated again, etc.

Fix by removing the old fd from the event queue before recreating it.
Merge pull request #657 from johto/fifo_recreation

Remove the old FIFO socket from the event queue when recreating it