- Some changes to the internals, including reverting some of the
recent changes to constructing values which turned out to be
more bother than it was worth.
- On C++11 compilers, better use of `construct` and `destroy`.
- Better testing.
[SVN r80350]
- Avoid an incorrect MSVC unused variable warning in the tests.
- Remove a `try..catch`.
- Adjust SFINAE use to try to supprt g++ 3.4. Fixes#7175.
- Fix some use of rvalues.
- Extra info in `at_tests`.
[SVN r79868]
