- static version of polyMesh::meshDir(), which takes a region name
polyMesh::meshDir(regionName)
vs
polyMesh::regionName(regionName)/polyMesh::meshSubDir
STYLE: use polyMesh::regionName(..) instead of comparing to defaultRegion
STYLE: use getOrDefault when retrieving various -region options
FIX: polyMesh::dbDir() now checks registry name, not full path (#3033)