[2/2] RFA: implement 'set print symbol'

[Eli Zaretskii]

> From: Tom Tromey <tromey@redhat.com>
> Date: Thu, 05 Apr 2012 12:03:32 -0600
> 
> Ok?

OK for the documentation part.  Although personally, I'm not happy
that from now on "set print sym TAB" will not auto-complete to a full
command, like it did before.  But that's me.

Thanks.