[RFC] constify ui_out_impl

[Joel Brobecker]

> This patch constifies ui_out_impl in struct ui_out, and various
> instances of ui_out_impl.
> 
> This removes a couple of FIXME comments (near cli_ui_out_impl and
> mi_ui_out_impl) that did not make sense to me.
> 
> Tested by rebuilding.
> 
> 2014-02-26  Tom Tromey  <tromey@redhat.com>
> 
> 	* cli-out.c (cli_ui_out_impl): Now const.  Remove comment.
> 	* cli-out.h (cli_ui_out_impl): Now const.
> 	* mi/mi-out.c (mi_ui_out_impl): Now const.  Remove comment.
> 	* ui-out.c (struct ui_out) <impl>: Now const.
> 	(default_ui_out_impl): Now const.
> 	(ui_out_new): Make 'impl' parameter const.
> 	* ui-out.h (ui_out_new): Update.

Not sure why the RFC, but the patch looks good to me.

For the FIXMEs, they seem to have been inherited from a bulk import
back in 2000, so we might have a tough time explaining them. Not sure
why it would make sense to initialize them dynamically, so I agree
with their removal...

-- 
Joel