[boost] shared_ptr<> and atomic_count

Hi- Looking at the implementation of shared_count<>, it seems as though it always uses a mutex for incrementing and decrementing the counter. Is there a reason why we aren't using atomic_count instead? In the worst case, it will have the same performance, but in the best case, it can be significantly faster (BOOST_USE_ASM_ATOMIC_H). Thanks. -- Colin Rafferty