bug fix: export of separate files for partitioned mesh wrote the indexing flag...

bug fix: export of separate files for partitioned mesh wrote the indexing flag (-2) for non-partition nodes, therefore exporting number. This is not valid for renumbered meshes. In any case the communication tables should be recomputed before exporting if the mesh is renumbered, this should moreover be done in a coherent fashion across partitions, so periodic boundaries will not be valid in this case.