[v3] install backwards headers in prefix

[Benjamin Kosnik]

> > If there are no major objections, I'd like to check this in today.
> 
> Yes, I object.  If you want to make it easier to use broken and 
> obsolete headers, add an option "-iobsolete" or something.  If 
> iostream.h is in the default directory, we will forever after get 
> questions about incompatibilities with standard features.  We need 
> a way to let those headers die peacefully.

You and I both.

The only other way around this, that I see, is to add /backward to the 
directories searched by g++. (You're -iobsolete idea is a bit vague.)

> You might also install an iostream.h in the regular directory
> containing only the line
> 
>   #error iostream.h is obsolete; try compiling with ``-iobsolete''.

In anycase, Alexandre mentioned the thought of adding 

#warning this header is deprecated, use <foo> instead of <foo.h>

to the top of the backwards foo.h headers.

I think this is a good idea.


-benjamin