message: Tweak GridFunction::GetTrueDofs and GridFunction::SetFromTrueDofs
  to avoid copies when the mesh is conforming.
diff: @@ -326,7 +326,7 @@ void GridFunction::GetTrueDofs(Vector &tv) const
  if (!R)
  {
  // R is identity -> make tv a reference to *this
  - tv = *this;
  + tv.MakeRef(const_cast<GridFunction &>(*this), 0, size);
  }
  else
  {
  @@ -341,10 +341,7 @@ void GridFunction::SetFromTrueDofs(const Vector &tv)
  const SparseMatrix *cP = fes->GetConformingProlongation();
  if (!cP)
  {
  - if (tv.Read() != data)
  - {
  - *this = tv;
  - }
  + *this = tv; // no real copy if 'tv' and '*this' use the same data
  }
  else
  {
  