test_rank_filter.cxx: Added two new test cases for the 2D case.
test_rank_filter.cxx: Added two new test cases for the 2D case.

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