FileManager (.ovm): Files with only valence-6 cells always identified as hexmeshes
FileManager::isHexahedralMesh
uses a very simplistic check to figure out if a file contains a hex mesh: if every cell has valence 6, it must be a hex mesh.
This leads to false positives, not only in the (less common) case of some unusual cells, but a hex mesh which was created and saved as polyhedral mesh, but not using the prescribed halfface order will be read as hex mesh, which causes all sorts of weird issues.
Not sure what the best way to fix this is!