* progmodes/octave.el (octave-variables): Remove. No builtin

* progmodes/octave.el (octave-variables): Remove.  No builtin
variables any more.  All converted to functions.
(octave-font-lock-keywords, octave-completion-at-point-function):
Fix uses.
(octave-font-lock-texinfo-comment): New user variable.
(octave-texinfo-font-lock-keywords): New variable for texinfo
comment block.
(octave-function-comment-block): New face.
(octave-font-lock-texinfo-comment): New function.
(octave-mode): Font lock texinfo comment block.