make SOCKET => lcb_socket_t on win32

This breaks binary compat with 2.x. However this is the correct and
proper thing to do. SOCKET tends to be an unsigned long on windows,
while it's an int on unix.

Change-Id: I6f718f53ab1f0faf59cef617c27505d5965ea98c
Reviewed-on: http://review.couchbase.org/35871
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>