[ET Trac] [Einstein Toolkit] #1589: suspicious code for operator+ in bboxset2

[Einstein Toolkit]

#1589: suspicious code for operator+ in bboxset2
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 Reporter:  rhaas   |       Owner:  eschnett           
     Type:  defect  |      Status:  new                
 Priority:  major   |   Milestone:                     
Component:  Carpet  |     Version:  development version
 Keywords:  Carpet  |  
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 Operator+ in bboxset2 seems to actually implement operator^ but I don't
 quite understand what they are all doing so, please review.

 When running with CARPET_DEBUG and CARPET_USE_BBOXSET2 the code dies with
 an assert due to a non-empty box intersection from inside CARPET_DEBUG
 code which seems to be due to the (invalid) assumption that multiple
 box.exterior would not overlap.

 Finally the last patch fixes an possible obscure issue where CarpetIOHDF5
 will ignore the checkpoint=no tag of a grid variable if the checkpoint
 file does indeed contain such a variable (since eg it was written with a
 code version that still had checkpoint=yes).

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1589>
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