BUG: errors found in feature-vtm merge !213

- vtkWrite with moving mesh was not updated the subsets properly,
  which caused it to crash.

- foamToVTK -overwrite ignored for single region cases,
  was working for multi-region cases

- minor documentation changes

applications/utilities/postProcessing/dataConversion/foamToVTK/foamToVTK.C

@@ -607,19 +607,24 @@ int main(int argc, char *argv[])
 
     if (Pstream::master())
     {
+        // Overwrite or create the VTK/regionName directories.
+        // For the default region, this is simply "VTK/"
+
+        fileName regionDir;
         for (const word& regionName : regionNames)
         {
-            // VTK/regionName  directory in the case
-
-            fileName regionDir;
             if (regionName != polyMesh::defaultRegion)
             {
                 regionDir = outputDir / regionName;
             }
+            else
+            {
+                regionDir = outputDir;
+            }
 
             if (args.found("overwrite") && isDir(regionDir))
             {
-                Info<< "Deleting old VTK files in "
+                Info<< "Removing old directory "
                     << regionDir.relative(runTime.globalPath())
                     << nl << endl;
                 rmDir(regionDir);

src/functionObjects/utilities/vtkWrite/vtkWrite.H

@@ -56,7 +56,7 @@ Description
             dome
             {
                 action  add;
-                shape   sphere;
+                source  sphere;
                 origin  (-0.1 -0.01 -0.1);
                 radius  0.25;
             }
@@ -98,7 +98,7 @@ Description
         directory   | The output directory name     | no | postProcessing/NAME
         width       | Padding width for file name           | no  | 8
         decompose   | Decompose polyhedral cells            | no  | false
-        writeIds    | Write cell/patch ids as field         | no  | true
+        writeIds    | Write cell/patch ids as field         | no  | false
     \endtable
 
     \heading Output Selection

src/functionObjects/utilities/vtkWrite/vtkWriteUpdate.C

@@ -157,8 +157,8 @@ bool Foam::functionObjects::vtkWrite::update()
     if
     (
         meshState_ == polyMesh::UNCHANGED
-     && !meshSubsets_.empty()
-     && !vtuMappings_.empty()
+     && (meshes_.size() == meshSubsets_.size())
+     && (meshes_.size() == vtuMappings_.size())
     )
     {
         return false;
@@ -174,7 +174,7 @@ bool Foam::functionObjects::vtkWrite::update()
 
         if (meshSubsets_.set(regioni))
         {
-            meshSubsets_.clear();
+            meshSubsets_[regioni].clear();
         }
         else
         {
@@ -200,9 +200,12 @@ bool Foam::functionObjects::vtkWrite::update()
         ++regioni;
     }
 
+    regioni = 0;
     for (auto& subsetter : meshSubsets_)
     {
         updateSubset(subsetter);
+        vtuMappings_[regioni].reset(subsetter.mesh());
+        ++regioni;
     }
 
     meshState_ = polyMesh::UNCHANGED;