LaTeX export: Protect secondary footnote references

LaTeX export: Protect secondary footnote references

Francesco Pizzolante writes:

> Exporting multiple references to the same footnote to LaTeX lead to a wrong
> generated code.
>
> The following example:
>
> --8<---------------cut here---------------start------------->8---
> * Title
>   This is my text[fn:1:This is my footnote.]. And another one[fn:1].
> --8<---------------cut here---------------end--------------->8---
>
> Will produce the following LaTeX code:
>
> --8<---------------cut here---------------start------------->8---
> \section{Title}
> \label{sec-1}
>
>   This is my text\footnote{This is my footnote. }. And another one\$$^{1}$\$.
> --8<---------------cut here---------------end--------------->8---
>
> The correct code should be:
>
> --8<---------------cut here---------------start------------->8---
> \section{Title}
> \label{sec-1}
>
>   This is my text\footnote{This is my footnote. }. And another one$^{1}$.
> --8<---------------cut here---------------end--------------->8---