consistent treatment of periodic and partition boundaries
Communication in parallel computations does not only involve exchanges on partition boundaries, currently explicitly written in the partitioned mesh file, but also on periodic faces/edges/points. In fact, these connections can transparently treated together.
It therefore makes sense to have periodic faces/edges/points explicitly included as partition boundaries (and potentially list their ghosts) if their match is located on another partition. Otherwise, this information has to be reconstructed with a preprocessor tool, or during the computation. The only way to do this reliably is a communication between all partitions, which becomes unfeasible for large scale computations, in particular in view of the allocation of storage buffers for the eager communication protocol, which are allocated at the first exchange between two partitions. Following creation during a global exchange to reconstruct periodic connections, most of those will then remain unused for the remainder of the computation.