Reintroduce support for `adaptive-fill-regexp' in paragraphs and comments

* lisp/org.el (org-adaptive-fill-function, org-fill-paragraph): Add
  support for `adaptive-fill-regexp' in paragraphs and comments.
* testing/lisp/test-org.el: Add tests.
Merge branch 'maint'
ox: Maintain compatibility with Emacs 23

* lisp/ox.el (org-export--dispatch-action): Maintain compatibility
  with Emacs 23.
Merge branch 'maint'
ox: Fix compilation error with Emacs < 24

* lisp/ox.el (org-export-stack-mode-map): Fix compilation error with
  Emacs < 24.
Merge branch 'maint'