automake: new option to print location of scripts and data files

automake: new option to print location of scripts and data files

With this change, we add a new automake option '--print-libdir'
that prints (on stdout) the path of the directory containing the
Automake-provided scripts (e.g., 'missing' and 'install-sh') and
data files (e.g., INSTALL or texinfo.tex).

Suggestion by Nick Bowler.  See also automake bug#10473.

* automake.in (parse_arguments): Handle the new option.
(usage): Mention it.
* doc/automake.texi (automake Invocation): Document it.
* NEWS: Update.
* tests/print-dir.test: New test.
* tests/list-of-tests.mk: Add it.