PATCH: fix dwarf2 handling of signed addresses

[Eric Christopher]

> The attached patch fixes that problem.  I can't apply it (no write
> privs -- but I do have a copyright assignment in place).
> 

This is enough to sponsor you for write approval. You've done work in
the past and appear to want to continue doing so. Go ahead and put in
the request with me as the sponsor.

> 2005-07-08  Paul Koning  <pkoning@equallogic.com>
> 
> 	* dwarf2.c (read_address): Check sign_extend_vma to handle targets
> 	where addresses are sign extended.

My only reservation for this is that we should be sign extending every
address no matter what and that this points to a bug in our code
elsewhere.

-eric