Added DataFileValue to SetEqualityIterator checks in conditional mutations

[dlmarion]

Fixes #3522

[dlmarion]

Supercedes #4175

[cshannon]

@dlmarion - A couple more things:

1. I am going to open a PR with my branch against your PR to make it easier to look at, but I noticed that the testFiles() test inside AmpleConditionalWriterIT is failing with this change here (without my changes as well) so I wanted to look at that.
2. I took a look at using BiFunction instead of two functions but I don't think that will work as that does the opposite of what we need. BiFunction takes 2 inputs and outputs 1 result but we need 1 input (the column) and to output 2 results (a key and value) that the iterator can concatenate transparently to the user when building the condition.

[cshannon]

I created a PR to your branch https://github.com/dlmarion/accumulo/pull/47

It fixes AmpleConditionalWriterIT as well, that test was failing because the changes here worked and the values were different. I updated the test to verify both the rejected and accepted case