build from tarball uses makeinfo

[Bruno Haible]

A build of poke-0.90 uses makeinfo:

$ make
...
/bin/bash /media/develdata/devel/build/poke-0.90/build-aux/missing makeinfo 
--plaintext ../../doc/poke.texi \
          > poke.text
...

While the GCS allow this (see
<https://www.gnu.org/prep/standards/html_node/Utilities-in-Makefiles.html>),
it is a best practice to avoid texinfo as a build prerequisite, by packaging
the generated files in the tarball. See
<https://www.gnu.org/prep/standards/html_node/Makefile-Basics.html>

Here is a proposed fix.

It also replaces a 'clean-local' target with a more declarative
'MOSTLYCLEANFILES' variable. Declarative is always better than procedural.

0001-Make-it-possible-to-build-the-tarballs-without-makei.patch
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