Add support for enabling SO_REUSEADDR when connecting to Redis and using
bind(). The following changes have been made:
* Added a new flag to the connection context indicating SO_REUSEADDR
  should be set.
* Added a max number of retries constant for when connect() hits
  EADDRNOTAVAIL.
* Added a new function, redisAsyncConnectBindWithReuse(), that let's
  clients enable this functionality.