added 2d checkerboard test (works only on tiger.princeton.edu)
added 2d checkerboard test (works only on tiger.princeton.edu)

PrincetonUniversity/seisflows,PrincetonUniversity/seisflows,luan-th-nguyen/seisflows_ndt,rmodrak/seisflows,rmodrak/seisflows,luan-th-nguyen/seisflows_ndt