bug#11422: automake 1.12 info doc installation problem

[Bruno Haible]

Hi Stefano,

> I see this report from you on the bug-texinfo list:
> 
>   <http://lists.gnu.org/archive/html/bug-texinfo/2012-05/msg00000.html>

It is a different issue. (But I happened to stumble across both bugs
at the same time.) The issue on bug-texinfo is a problem with an INFOPATH
that contains at least two directories.

This issue here is about stale entries that refer to nonexistent nodes, when
installing a new Automake release using the same --prefix as an older one.

How to reproduce:
1. $ mkdir /tmp/inst
2. Install automake-1.11.2:
   $ tar xvfz .../automake-1.11.2.tar.gz
   $ (cd automake-1.11.2 && ./configure --prefix=/tmp/inst && make && make 
install)
3. $ INFOPATH=/tmp/inst/share/info info automake
   works
4. Install automake-1.12 with the same --prefix:
   $ tar xvfz .../automake-1.12.tar.gz
   $ (cd automake-1.12 && ./configure --prefix=/tmp/inst && make && make 
install)
5. $ INFOPATH=/tmp/inst/share/info info automake
   fails, it produces the manpage fallback.

Bruno