RFC: implement "catch signal"

[Eli Zaretskii]

> From: Tom Tromey <tromey@redhat.com>
> Date: Fri, 16 Nov 2012 12:06:40 -0700
> 
> This patch implements "catch signal".  I took Pedro's unfinished "catch
> signal" patch and worked on it a bit.
> 
> This needs a doc review at least.

Thanks.  The doc is OK, with the exception of one comment:

> +When a signal is caught by a catchpoint, the signal's @code{stop} and
> +@code{print} settings, as specified by @code{handle}, are ignored.
> +However, whether the signal is still delivered to the inferior depends
> +on the @code{pass} setting; this can be changed in the catchpoint's
> +commands.

I suggest to make the last part of this less vague, by saying _how_
that can be changed.