New function for traversing sub boundaries.

AMDiS/src/ElInfo.h

AMDiS/src/Element.h

AMDiS/src/Line.cc

AMDiS/src/Line.h

AMDiS/src/Tetrahedron.cc

AMDiS/src/Tetrahedron.h

AMDiS/src/Triangle.cc

AMDiS/src/Triangle.h

AMDiS/src/est/ResidualEstimator.cc

AMDiS/src/est/ResidualEstimator.h

AMDiS/src/est/SimpleResidualEstimator.cc

AMDiS/src/parallel/InteriorBoundary.h

test/mpi/data/data0007/bound_rank_0.dat

test/mpi/data/data0007/bound_rank_1.dat

test/mpi/data/data0007/bound_rank_2.dat

test/mpi/data/data0007/bound_rank_3.dat

test/mpi/init/test0007.dat.2d

test/mpi/src/test0007.cc