LDAP C API: LDAP_OPT_DESC

["Kurt D. Zeilenga" <Kurt@OpenLDAP.Org>]

It just occurred to me that the underlying implementation may not actually
utilize sockets and hence not be able to return the underlying I/O descriptor.
It also may be possible for socket descriptors to be something different than
'int'.  IIRC, I believe it's a pointer under MacOS.

It might be wise to be generalize or remove LDAP_OPT_DESC.  (I should
note that some APIs have already introduced a generic "socket" type).

To generalize LDAP_OPT_DESC, I would suggest adding:
	typedef impl_socket_t ber_socket_t;

   Implementations MUST replace impl_socket_t with an appropriate
   type.  Implementations returning I/O descriptors SHOULD replace impl_socket_t
   with a suitable type for I/O descriptors.  Implementations which do not
   return I/O descriptors SHOULD replace impl_socket_t with int and MUST always
   return LDAP_OPT_ERROR.  Returning I/O descriptors is RECOMMENDED.