Add a third mode to "breakpoints always-inserted", and make it the default

[Eli Zaretskii]

> From: Pedro Alves <pedro@codesourcery.com>
> Date: Tue, 12 Aug 2008 00:34:24 +0100
> 
> So, this patch changes the "set breakpoints always-inserted" setting to
> be a three-state.  on and off, the same as before, and a new mode,
> "follow-non-stop".

How about calling this state "auto"?

> In the latter mode, GDB will behave as "on", if
> we're in non-stop mode, and as "off" if we're in all-stop mode.

I think _behave_ as "on" is not a good idea.  I suggest that it
actually _set_ the option "on".  That way, code elsewhere will need
only to look at a single option, and won't need to know that if the
value is follow-non-stop, it needs to check another flag.

> +This is the default mode.  If gdb is controlling the inferior in
> +non-stop mode (@pxref{Non-Stop Mode}), gdb behaves as if
> +always-inserted mode is on.  If gdb is controlling the inferior in
> +all-stop mode, gdb behaves as if always-inserted mode is off.

We don't use a literal "gdb" in the manual, we use "@value{GDBN}".

Also, it would be helpful to have an index entry here, something like

  @cindex non-stop mode, and @code{breakpoint always-inserted}