message: Add support for DXT2 / DXT4 aliases of DXT3 (BC2) and DXT5 (BC3)
  * The only difference in these is whether or not pre-multiplied alpha is assumed
  to be used, and that doesn't change the actual data - only the interpretation.
diff: @@ -937,9 +937,11 @@ dds_data load_dds_from_file(FILE *f)
  case MAKE_FOURCC('D', 'X', 'T', '1'):
  ret.format = DXGIFormat2ResourceFormat(DXGI_FORMAT_BC1_UNORM);
  break;
  + case MAKE_FOURCC('D', 'X', 'T', '2'):
  case MAKE_FOURCC('D', 'X', 'T', '3'):
  ret.format = DXGIFormat2ResourceFormat(DXGI_FORMAT_BC2_UNORM);
  break;
  + case MAKE_FOURCC('D', 'X', 'T', '4'):
  case MAKE_FOURCC('D', 'X', 'T', '5'):
  ret.format = DXGIFormat2ResourceFormat(DXGI_FORMAT_BC3_UNORM);
  break;
  