Remove confusion of C-c C-o in footnote with cursor on link

Remove confusion of C-c C-o in footnote with cursor on link

* lisp/org.el (org-open-at-point): Don't do footnote action if cursor is
on a bracket link.

Sebastian Mengin writes:

> Hi,
>
> Consider the following minimal example:
>
> Text[fn:1]
>
> * Footnotes
> [fn:1] Note with a [[file:abecedaire.jpg][link]].
>
> Here with orgmode 7.02, doing C-c C-o on the link moves the cursor on
> [fn:1] and says in the minibuffer: "Position saved mark to ring, go back
> with C-c &", instead of opening the linked file.
>
> Is this a bug?
>