[v3] install backwards headers in prefix

[Gabriel Dos Reis]

Alexandre Oliva <oliva@lsd.ic.unicamp.br> writes:

| On Dec 15, 2000, Nathan Myers <ncm@nospam.cantrip.org> wrote:
| 
| > The "-iobsolete" flag would add $(prefix)/backward to the set of
| > directories searched by g++, as you say.  I just don't want that to 
| > happen by default.  (It might be "-ibackward", instead, for consistency, 
| > or $(prefix)/backward might be changed to $(prefix)/obsolete.)
|  
| I'm ok with doing it *after* we've had a release in which people are
| just warned.  We don't want to go out gratuitously breaking
| everybody's previously-working C++ code.  Warn first, give them time
| to adjust their programs, and only then disable the feature by
| default.

I'm a bit between Nathan's position and Benjamin's:  That is provide
an option to turn off backward headers; and in subsequent release make
it the default, and eventually remove them completely. Obviously, we
should be warning in the next release.

-- Gaby
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