Add a couple new classes for managing committing scans consistently.
Propagate those around in place of various ad-hoc variations.
Adjust constructor a little to make testing easier.
Add the minimal IT for that.
Need to track current and total counts separately.
Copy/paste error.
merge MMcM: Factor out committing scan cursors

Merge pull request #1564 from MMcM/sql-layer/fdb-scan-transaction-options
https://github.com/FoundationDB/sql-layer/pull/1564