substitute gdb convenience variable into gdb command

[Michael Snyder]

On Tue, 2008-02-12 at 14:55 -0500, Daniel Jacobowitz wrote:
> On Tue, Feb 12, 2008 at 11:41:33AM -0800, Michael Snyder wrote:
> > Hmm!  That's a bit of an oversight...
> > thread_apply_command calls strtol.  It ought to call
> > one of the built-in expression parsing functions.
> 
> Not really.  It would become pretty much impossible to parse the
> command if you did that.  There's no reliable way to find the end of
> an expression if it has unknown text afterwards.

You're right.  I ran into the same issue when I did the
dump and restore commands.  I used parse_and_eval_long, 
but only because I arranged the command syntax so that
the integer value was the last argument on the command line.

In this case it isn't the last argument, so we can't do that.