A bunch of plumbing to get the AIS column from the optimizer to the Postgres row description.
Similar to what the embedded JDBC driver (JDBCResultSetMetaData.ResultColumn) already did.
merge MMcM: AIS column from the optimizer to the Postgres row description

Merge pull request #1487 from MMcM/sql-layer/pg-result-column-ais-column
https://github.com/FoundationDB/sql-layer/pull/1487