message: demo: Fix generatePlane indices
  The test mesh was not generated properly; fortunately, the plane mesh in
  vcachetester was generated using unrelated - and correct - code, so this
  does not invalidate any experimental results.
diff: @@ -42,13 +42,13 @@ Mesh generatePlane(unsigned int N)
  for (unsigned int y = 0; y < N; ++y)
  for (unsigned int x = 0; x < N; ++x)
  {
  - result.indices.push_back((y + 0) * N + (x + 0));
  - result.indices.push_back((y + 0) * N + (x + 1));
  - result.indices.push_back((y + 1) * N + (x + 0));
  + result.indices.push_back((y + 0) * (N + 1) + (x + 0));
  + result.indices.push_back((y + 0) * (N + 1) + (x + 1));
  + result.indices.push_back((y + 1) * (N + 1) + (x + 0));
  - result.indices.push_back((y + 1) * N + (x + 0));
  - result.indices.push_back((y + 0) * N + (x + 1));
  - result.indices.push_back((y + 1) * N + (x + 1));
  + result.indices.push_back((y + 1) * (N + 1) + (x + 0));
  + result.indices.push_back((y + 0) * (N + 1) + (x + 1));
  + result.indices.push_back((y + 1) * (N + 1) + (x + 1));
  }
  return result;
  