RFA: implement all missing macro expansion features

[Eli Zaretskii]

> Cc: gdb-patches@sourceware.org
> From: Tom Tromey <tromey@redhat.com>
> Date: Sat, 20 Sep 2008 15:54:51 -0600
> 
> In the interest of full disclosure, there is another pedantic error
> case that this code does not handle: it is invalid to attempt to paste
> two things which do not form a token.  I did not implement checking
> for this -- but perhaps you would want that?
> 
> I think this patch addresses all your concerns.  I also incorporated a
> documentation update, which was sitting unsubmitted in my patch queue.

Thanks.  I think we also need a NEWS entry.