Look into adding API operation to return non existant row columns.

[keith-turner]

A few times I have written Fluo code to find the row columns that do not exists. A primitive operation for this could be optimized.

[keith-turner]

I deleted the comment I had made here because I was thinking of #527 when I wrote that comment. I copied the comment that was here to #527 and modified it a bit. I realized setIfAbsent() doing something similar to delete() would not work, so I changed that when copying.

I wish I had recorded the use case I was thinking of for this operation, because I can't remember. It may be that if setIfAbsent() is available then there is no use case for this operation. I think it it would be good to defer this until there is a use case is identified that is not efficiently satisfied by setIfAbsent()

[kennethmcfarland]

I would like to claim this if possible. The other issues I have currently are fairly trivial.