CCBC-407: Increase performance on select

- fd_set is itself a bit array. Do not allocate an array of these
- select should use the maximum fd +1 as its first argument, not
  FD_SETSIZE

Change-Id: I64f1f551e750e52767da47642b0e36efce38b3bc
Reviewed-on: http://review.couchbase.org/37388
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>