* configure.in: Replace nonstandard CHECK_STDARG with

* configure.in:  Replace nonstandard CHECK_STDARG with
AC_CHECK_HEADERS.  Also check for header file macsock.h, which
is a dummy test -- it's false on Unix and PC's, but on the Mac
we hand-configure it to be true, to indicate that we want Mac
socket support rather than Unix socket support.
* base-defs.h, k5-config.h:  Use HAVE_STDARG_H, not STDARG_PROTOTYPES.
* k5-config.h (NEED_SOCKETS):  Add new section which brings in
socket include files for the appropriate compilation environment
(Mac or Unix; Windows already did this).
* macsock.h:  New include file, derived from Cygnus Network Security
Mac K4 release, for simulating sockets under MacTCP.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@5140 dc483132-0cff-0310-8789-dd5450dbe970