configure guesses wrong "install" for AIX

[David Edelsohn <dje at watson dot ibm dot com>]

	I thought that we had fixed the problem of configure choosing
/usr/bin/installbsd for AIX, but I notice that configure continues to use
one of the AIX install programs instead of choosing "install-sh".  The
test in configure seems to be:

        if test -f $ac_dir/$ac_prog; then
          if test $ac_prog = install &&
            grep dspmsg $ac_dir/$ac_prog >/dev/null 2>&1; then
            # AIX install.  It has an incompatible calling convention.
            # OSF/1 installbsd also uses dspmsg, but is usable.
            :
	  else

However, the string "dspmsg" no longer is present in the executable, so
that is a worthless test.  AIX no longer uses some script, so grepping the
executable is pretty silly.

	None of the AIX install programs work correctly and configure
discovers that the host is AIX early on, so I think that install-sh should
be set early for AIX.

David