[PATCH doc/langref.tex] Add error probe information

[Josh Stone]

On 09/03/2009 03:18 PM, Robb Romans wrote:
> +\subsubsection{error}
> +\index{error} The \emph{error} probe point is similar to the end
> +probe, except the probe handler runs when the session ends if an error
> +occurred.  In this case, an \texttt{end} probe is skipped, but each
> +\texttt{error} probe is still attempted.  You can use an
> +\texttt{error} probe to clean up or perform a final action on script
> +termination. You can also numerically parametrize an \texttt{error}
> +probe to set a sequence.

The meaning of the sequence isn't really clear until its described in
the next subsection for begin and end probes.  Perhaps the error
sequence should be moved into that discussion?

Thanks,

Josh