[PATCH v2] Add convenience variable $_exitsignal

[Eli Zaretskii]

> From: Sergio Durigan Junior <sergiodj@redhat.com>
> Cc: gdb-patches@sourceware.org, dje@google.com, palves@redhat.com
> Date: Tue, 18 Jun 2013 16:02:48 -0300
> 
> I could say "sets $_exitcode to @code{void}" instead, WDYT?

I'd use "resets", but otherwise this sounds fine, thanks.