Since the nis headers are broken on HPUX 11.00, AIX 4.3 and 5.1 
a propose a workaround.


The workaround is tested on quite a few Unices and Linuxes: Linux (Redhat 7.1
and 9), Solaris 5.6, Solaris 8, AIX4.3, AIX 5.1, HPUX 10.20, HPUX 11.00, HPUX
11.22, IRIX 6.5. FreeBSD 4.7. In short: it should behave correctly.

1) 

HPUX 11.00: yp_match is declared 
/usr/include/rpcsvc/ypclnt.h:extern int yp_match(char *, char *, char *, int,
char **, int *);

That's a problem for HP's own C-compiler: the const argument user_name from
automount_lookup(), which is tried to pass non-const to yp_match.

I propose the remove the const from automount_lookup argument. (It must be
removed from both implementations, otherwise different conflicting headers show
up in includes/proto.h)

And two problems for AIX-5.1 (and AIX-4.3)

2) <rpcsvc/ypclnt.h> is not shielded with #ifndef against multiple inclusion.
proposed patch to remove the #include "rpcsvc/ypclnt.h", it is included in
include/includes, anyway.

3) The struct ypall_callback is only declared forward in  <rpcsvc/yp_prot.h>.
therefore I get compiler error with xlc. changing the order of declaration fixes
this.