rank_filter.hxx: Changed to use Boost's memory optimized multiset.
rank_filter.hxx: Changed to use Boost's memory optimized multiset.

DudLab/rank_filter,jakirkham/rank_filter,jakirkham/rank_filter,nanshe-org/rank_filter,nanshe-org/rank_filter,DudLab/rank_filter,jakirkham/rank_filter,nanshe-org/rank_filter,DudLab/rank_filter