RFC: implement 'info proc mappings' for core files

[Eli Zaretskii]

> From: Tom Tromey <tromey@redhat.com>
> Cc: gdb-patches@sourceware.org
> Date: Tue, 20 Nov 2012 13:05:33 -0700
> 
> Here's a version of the patch that just updates the documentation to
> follow the code.
> 
> The reason I think supporting a subset of "info proc" for core files is
> a reasonable thing to do is that we're basically viewing a snapshot of
> the relevant parts of /proc as written out when the process died.
> 
> This needs a doc review.

The documentation parts are OK.  Thanks.