autoheader: check templates of all config headers
* bin/autoheader.in: When checking for missing templates, take
all config headers into account, not just the one generated by
autoheader. This makes it possible to use AC_DEFINE() for
secondary headers without duplicating the template into the
first header.
* tests/tools.at: Add a check for autoheader with multiple
config headers.
* NEWS: Document the new behavior.
Message-Id: <
1482336946.31331.2.camel@gmail.com>
Signed-off-by: Eric Blake <eblake@redhat.com>