Specify .texi encoding.

Specify .texi encoding.

* emacs-lisp-intro.texi:
* back.texi, book-spine.texi, lay-flat.texi:
* ada-mode.texi, auth.texi, autotype.texi, bovine.texi, calc.texi:
* cc-mode.texi, cl.texi, dbus.texi, dired-x.texi, ebrowse.texi:
* ede.texi, ediff.texi, edt.texi, efaq.texi, eieio.texi:
* emacs-gnutls.texi, epa.texi, erc.texi, ert.texi:
* eshell.texi, eudc.texi, flymake.texi, forms.texi, gnus-coding.texi:
* gnus-faq.texi, htmlfontify.texi, idlwave.texi, ido.texi, info.texi:
* message.texi, mh-e.texi, newsticker.texi, nxml-mode.texi:
* octave-mode.texi, org.texi, pcl-cvs.texi, pgg.texi, rcirc.texi:
* reftex.texi, remember.texi, sasl.texi, sc.texi, semantic.texi:
* ses.texi, sieve.texi, smtpmail.texi, speedbar.texi, srecode.texi:
* todo-mode.texi, tramp.texi, url.texi, vip.texi, viper.texi:
* widget.texi, wisent.texi, woman.texi:
Add @documentencoding.