[Build-common-hackers] Bug#217131: new patch, add libtool-update facility

[Stefan Gybas]

Robert Millan wrote:

> I updated the autotools-update patch to update libtool also. It can be
> made to update libtool properly using "libtoolize" when
> DEB_AUTO_UPDATE_LIBTOOL="pre", or it can also update libtool after it
> is generated (discouraged, but it might be useful on some situations)
> when DEB_AUTO_UPDATE_LIBTOOL="post".

I think this should be in autotools-files.mk instead of autotools.mk, 
like the code for updating config.{guess,sub}. The possible changes 
should also be undone in the clean target.

If nobody disagrees, I'll put it in autotools-files.mk.

Stefan