Cross-port exception-safety and move fixes of std::any to std::experimental::any.

Cross-port exception-safety and move fixes of std::any to std::experimental::any.

Cross-port exception-safety and move fixes of std::any to
std::experimental::any.
* include/experimental/any (operator=(const any&)):
Make strongly exception-safe.
(operator=(any&&)): clear() unconditionally in the case where
rhs has a value.
(_Manager_internal<_Tp>::_S_manage): Move in _Op_xfer, don't copy.
* testsuite/experimental/any/assign/2.cc: Adjust.
* testsuite/experimental/any/assign/exception.cc: New.
* testsuite/experimental/any/cons/2.cc: Adjust.
* testsuite/experimental/any/misc/any_cast_neg.cc: Ajust.

From-SVN: r241479