Draft: Problem with reverse secondary index iterator after primary_index.erase()

There is a unit test named testIteration2A that is failing. Although it hasn't been winnowed down, the test might still be simple enough for debugging.

0. The unit test initializes a table with four items.
1. It removes an item from the "middle" of a secondary index iterator.
2. It removes another item from the beginning of a reverse secondary index iterator.
3. It does not encounter the expected item for the the first item of the reverse secondary index iterator.