[RFA, doc RFA] Change "set debug symtab-create" to accept verbosity levels

[Eli Zaretskii]

> From: Doug Evans <dje@google.com>
> Date: Fri, 27 Sep 2013 16:37:46 -0700
> 
> The output of "set debug symtab-create 1" is too verbose for my tastes.
> Including every header in the output reduces the S/N ratio too much.
> 
> This patch changes "set debug symtab-create" to accept a verbosity level.
> 
> Regression tested on amd64-linux.
> 
> Ok to check in?

OK for the documentation parts.

Thanks.