Fix LaTeX-newline when comment-auto-fill-only-comments is non-nil.

* latex.el (LaTeX-newline): Fix for when
`comment-auto-fill-only-comments' is non-nil.  Suggested by Piet
van Oostrum.
Build HTML doc with makeinfo if texi2html is not available.

* doc/Makefile.in: Make it possible to build the HTML doc with
`makeinfo' if `texi2html' is not available.  Add new
`TEXI2HTML_TOC' variable.
(extradist): Use `TEXI2HTML_TOC'.
(html/$(TEXI2HTML_TOC)): Use `TEXI2HTML_TOC'.  Fix splitting
option to HTML engine.  Suggested by Norbert Preining.
Update for upcoming release.

* RELEASE: Update AUCTeX version, the new features section, and
the list of contributors.

* configure.ac: Update AUCTeX version.

* doc/changes.texi: Mention generic bug fixes for 11.88 release.

* doc/tex-ref.tex: Update AUCTeX version and copyright years
across the file.
Add now working `TeX-previous-error' key-binding.

* tex.el: Update copyright year.