[patch] stephen's staging headers patch

[Benjamin Kosnik]

> I don't have access to the sources right now, but I hit a problem in which
> the numeric_limits stuff was regenerated every time, which caused everything
> that depended on it to be remade every time, at least for native compiles.  On
> my pokey system that was strong motivation to fix things.  Off the top of my
> head, there was just a few lines in the Makefile, they could be posted as a
> patch later if you want to put your changes in sooner.

Nope that's what I'm seeing too: gen_numeric_limits is always run. 

If you could post the patch, please let me know. I'd like to try and get 
this patch in within the next week.

I did some work on this patch too, but didn't provide a ChangeLog entry, 
sadly. It does work, but let's try to clean up the known issues before 
it's checked in.

-benjamin