TakeUntil with CancellationToken #2222
                
     Merged
            
            
          
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Resolves #2181
This takes the changes from #2182 and fixes the minor issues (use of block-scoped vs file-scoped namespaces, a typo, and the spelling we mostly use for Cancelled). @nilsauf, the author of #2182 is currently on vacation, so I'm making these changes to enable this to get merged sooner, and into the 6.1 release