[boost] [serialization] non-virtual destructors in 1.33.1

Between 1.33 and 1.33.1_beta, several classes in the serialization library were changed from having virtual destructors to having non-virtual destructors. An example is basic_oserializer. Many of these classes have virtual functions, with the result that "g++ -Wall" now complains about them ("has virtual functions but non-virtual destructor"), so that I now get tons of warnings when compiling code that uses the serialization library. My guess would be that none of these warnings are actually interesting, but that belief doesn't really help all that much. Was there a good reason for this change? Could it be reverted? If not, is there some other thing that could be done to eliminate these warnings? For 1.33.1 release?