Zones: Now derived from PtrListDictionary to provide faster lookup

Now the HashTable underlying PtrListDictionary is used for zone lookup by name
which is a lot faster than the linear search method used previously if there are
a large number of zones.

applications/utilities/postProcessing/dataConversion/foamToEnsight/ensightMesh.C

@@ -261,7 +261,7 @@ void Foam::ensightMesh::correct()
     // faceZones
     if (faceZones_)
     {
-        wordList faceZoneNamesAll = mesh_.faceZones().names();
+        wordList faceZoneNamesAll = mesh_.faceZones().toc();
         // Need to sort the list of all face zones since the index may vary
         // from processor to processor...
         sort(faceZoneNamesAll);