[21.5] Use .../share instead of .../lib for datadir

[Stephen J. Turnbull]

QUERY

Michael Sperber writes:

 > I'll commit Thursday if nobody objects.

Wow, that was easy.  I mean, small diffstat, not the amount of work
and checking.  Sorry, I don't have time to deal with this until the
weekend; guess I'll just have to trust you. :-P

What happens if you have an existing 21.5.28 installation, and then
have an attack of blondeness and install having updated to your patch?

Ie, do you just get lispy cruft in $prefix/lib/xemacs-21.5.28/$arch
that you can remove with rm -rf $prefix/lib/xemacs-21.5.28/$arch/lisp
at some later date without any problems, or is there any possibility
that that could end up on the load-path?

 > 	Also, define AC_DATAROOTDIR_CHECKED to shut up autoconf.

I'm not sure this is a good idea.  Is there a reason why we can't be
datarootdir compliant (besides Just Saying No To Drugs)?  If not,
shouldn't we flagellate ourselves with the warning until we are?