vtkSortedTableStreamer: avoid merging blocks
vtkSortedTableStreamer merges blocks into a single table. That was okay in the past when the spreadsheet view only showed data from one block at a time. Now that support showing all blocks by default, that can cause considerable slow down when dealing with large data. We should change the implementation to avoid that.
cc: @boonth, I think this explains the slowdown you were seeing with spreadsheet view.