Avoid obstack_free in cp-namespace.c

[Eli Zaretskii]

> From: Elena Zannoni <ezannoni@redhat.com>
> Date: Mon, 9 Feb 2004 17:39:19 -0500
> 
> For the curious, you might as well explain the whole story.

Thanks.  It would be nice if this could find its way into
gdbint.texinfo, sigh...