Jack Jansen: The GUSI 2.0 I/O library used on the Mac uses the

socklen_t (unsigned int) for most size parameters.  Apparently this is
part of the UNIX 98 standard.

[GvR: the changes to configure.in etc. that I just checked in make
sure that socklen_t is defined everywhere, so I deleted the little
part of Jack's mod to define socklen_t if not in GUSI2.  I suppose I
will have to add it to the Windows config.h in a minute.]