Update autoconf version requirement in install.texi

[Roland McGrath]

> (With the aclocal.m4 change two years ago to require an exact autoconf 
> version, and then with the more recent increase of that version, that is.)

Phew, so it was your fault before it was mine!  Such a relief.
(We won't discuss how much entirely and completely my fault the
entire set of concepts leading to GLIBC_PROVIDES is.)

> > aclocal.m4 reminding one to update install.texi to match.  (Or feel free to
> > get crazy with a generated file of Texinfo macros!)
> 
> I've committed this patch.
> 
> 2014-10-31  Joseph Myers  <joseph@codesourcery.com>
> 
> 	* aclocal.m4 (GLIBC_AUTOCONF_VERSION): Mention need to update
> 	install.texi in comment.

OK, fine, be that way.  I've clearly failed to pass on to the community the
penchant for ludicrous over-scripting auto-generation mania that was the
hallmark of my authorship, so I'll have to stick around a few more years
and keep wearing you down.