texinfo: update to 6.7

texinfo: update to 6.7

Full changelog as retrieved from https://git.savannah.gnu.org/cgit/texinfo.git/plain/NEWS:

6.7 (23 September 2019)
* Language:
  . support of index subentries and sub-subentries with @subentry
  . new commands @seeentry and @seealso in index entries
  . no need to wrap Top node in @ifnottex - omitted automatically when
    processed with TeX
  . UTF-8 is the default input encoding

* texi2any
  . for HTML output, mark index nodes in menus and tables of contents
    with the 'rel' attribute of the 'a' tag.
  . TOP_NODE_UP is now only used in HTML if TOP_NODE_UP_URL is set.
    Also TOP_NODE_UP should now be formatted in the output format.
    In HTML TOP_NODE_UP should be suitable for inclusion in HTML
    element attributes, so for instance should not contain elements.
  . support of noderename.cnf files has been removed
  . INPUT_PERL_ENCODING, INPUT_ENCODING_NAME, NODE_FILE_EXTENSION,
    NODE_FILENAMES, SHORTEXTN and TOP_NODE_FILE removed as customization
    variables.
  . TOP_NODE_FILE_TARGET now contains the extension.
  . error messages translated when the XS parser module is in use

* texi2dvi
  . unconditionally run in --batch mode, i.e. without stopping if there
    is a TeX error
  . keep on going after a TeX error if the index files changed
  . with --tidy (or --build-dir), avoid reading index files from previous
    runs where --tidy was not used

* info
  . for a tree search (with M-/), '}' and '{' work as well as 'M-}' and
    'M-{' to go through the results

* Distribution:
  . Several obsolete portability checks removed
  . gettext 0.20.1, automake 1.16.1

No rootfile changes were necessary.

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>