versioning C++ includes

[B. Kosnik]

> I think the binary compatibility issues are incorporated in the
> installed .so (or .a) name -- existing practice.  As far as source
> code is concerned, it suffices to use the compiler release number. 

Yep. This is correct. Phil's symbol versioning bits implemented this for
libstdc++ 3.1.0 on systems that use GNU ld, have shared libgcc, etc.
Perhaps Phil can clarify or elaborate? Nathan, if you compile to object
file (-c) with gcc-3.1.0 and do 'nm' on the undefined (and thus linked)
symbols you'll see the versioning info. It's much as you desire,
already.

So, the only thing left is include versioning, as far as I'm concerned. 

At that point, the library ABI bits can be fully detailed. I posted an
outline a bit ago, but it's just a sketch.

-benjamin