Made bad_weak_ptr to derive std::exception as public base.
Made bad_weak_ptr to derive std::exception as public base.

retrieva/pficommon,retrieva/pficommon,retrieva/pficommon,pfi/pficommon,retrieva/pficommon,takei-yuya/pficommon,takei-yuya/pficommon,retrieva/pficommon,pfi/pficommon,pfi/pficommon,pfi/pficommon,takei-yuya/pficommon,takei-yuya/pficommon