* lib/am/texibuild.am (%DEST_PREFIX%%DEST_SUFFIX%): Rename as ...

* lib/am/texibuild.am (%DEST_PREFIX%%DEST_SUFFIX%): Rename as ...
(%DEST_INFO_PREFIX%%DEST_SUFFIX%): ... this, and honor ?INSRC?
to select $(srcdir) or `.' builds.
(INFO_DEPS): Define here.
* lib/am/texinfos.am (dist-info): Strip filename starting with
"$(srcdir)/".
* automake.in (output_texinfo_build_rules): Take a new argument
$insrc, and adjust substitutions in 'texibuild'.
(handle_texinfo_helper): Compute a regex of all user-cleaned
files, and use this to select whether to build .info files in `.'
or $(srcdir).  Give an account of the $(srcdir) vs `.' debacle.
Alway build the version.texi and stamp files in $(srcdir).  Do not
define INFO_DEPS.
* tests/Makefile.am (TESTS): Add txinfo23.test, txinfo24.test,
and txinfo25.test.
* tests/txinfo23.test, tests/txinfo24.test, tests/txinfo25.test:
New files.
* tests/txinfo13.test, tests/txinfo16.test, tests/txinfo3.test,
tests/vtexi.test: Adjust to new rules.