[Orgmode] [BUG] htmlp and latexp

[Dan Davison]

Commit ed6d6760268 removed variables htmlp and latexp from
`org-export-preprocess-string'. Nothing wrong with that, but I think it
has broken export for those using org-special-blocks, which contains

#+begin_src emacs-lisp
(defvar htmlp)
(defvar latexp)
(defun org-special-blocks-make-special-cookies ()
  "Adds special cookies when #+begin_foo and #+end_foo tokens are
seen.  This is run after a few special cases are taken care of."
  (when (or htmlp latexp)
    (goto-char (point-min))
...
#+end_src

I think because those defvars lack a second argument, the variable is
not actually defined, i.e. they're not equivalent to (defvar htmlp nil).

IIuc htmlp and latexp occur occasionally in org code as somewhat
unofficial ways to test "am I in the middle of export?".

They also occur in org-exp-blocks, but in deprecated code, so not a
priority to fix.

Dan