typedef evutil_socket_t to int when libevent version is less than 2.x

Change-Id: I0ae641e298fdfd9bbe9078dd8051af722de17cb9
Reviewed-on: http://review.couchbase.org/32604
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>