[PATCH v4] Implement $_exitsignal

[Eli Zaretskii]

> From: Sergio Durigan Junior <sergiodj@redhat.com>
> Cc: Doug Evans <dje@google.com>, Pedro Alves <palves@redhat.com>
> Date: Tue, 17 Sep 2013 14:50:21 -0300
> 
> +To distinguish between whether the program being debugged has exited
> +(i.e., @code{$_exitcode} is not @code{void}) or signalled (i.e.,
> +@code{$_exitsignal} is not @code{void}), the convenience function
> +@code{$_isvoid} can be used (see @ref{Convenience Funs,, Convenience
> +Functions}).

@pxref would be better here than "see @ref".

Otherwise, the documentation part is OK.

Thanks.