Long-term plan for C++98/C++11 incompatibility

[Jonathan Wakely]

P.S. we already document how to link applications using two
incompatible versions of libstdc++:
http://gcc.gnu.org/onlinedocs/libstdc++/manual/abi.html#abi.testing.multi

(whether you can actually make that work in practice is another matter!)

The situation is similar for C++98 and C++11 code, if the incompatible
standard library types aren't used in the library interfaces then they
should be able to coexist and not interfere.

If in a future release we use namespace and/or symbol versioning to
keep the c++98 and c++11 code distinct then they could coexist in the
same library and won't interfere at all.