Improve the autotools spkg (#13557) needs review

[Jeroen Demeyer]

I have made a lot of fixes to my autotools spkg, essentially improving
it from a "proof of concept" to a "real" spkg. For this reason, I would
like to move the package from experimental to optional.

The main change is that the package now ships an auto-generated Makefile
to build the various different versions of autotools, with correct
dependencies (e.g. autoconf-2.62 depends on automake-1.10). This made
the packaging process a lot more involved, but the spkg-install is much
simplified (it essentially just executes make).

I added Texinfo to the package, since that's a prerequisite and it's
also often used for bootstrapping packages, so it fits with the theme.

There are also a lot of small fixes to make the package more portable,
it no longer requires GNU-specific tools. Indeed, it now builds on all
buildbot systems that I tried (sage, rosemary, iras, bsd, moufang, mark,
hawk).

Please review this *optional* package:
http://trac.sagemath.org/sage_trac/ticket/13557

Thanks,
Jeroen.

[Jeroen Demeyer]

Could somebody please review this optional package? I think it's a
useful improvement over the old autotools spkg.