Update and fix instructions and scripts for updating the Web pages

Update and fix instructions and scripts for updating the Web pages

* admin/admin.el (manual-html-fix-index-2): Support Texinfo 6.8
and later by not converting TOC menus into tables.  (Bug#49719)
* admin/upload-manuals (New directory): Invoke "cvs add" in
$webdir, to pick up the correct CVSROOT.
* admin/make-tarball.txt: Update the section about the Emacs Web
pages.

* etc/refcards/Makefile (pl-refcard.dvi): If mex.fmt cannot be
found, invoke 'mex' instead of 'tex'.