Clean out all inactive AIS generations, not just those older than the oldest.
merge MMcM: Clean out all inactive AIS generations, not just those older than the oldest

Merge pull request #1210 from MMcM/sql-layer/sql-ais-active-generations
https://github.com/FoundationDB/sql-layer/pull/1210
Add a transaction service API to check for rollback errors at commit whose success state is unknown.
Not implemented for Persistit.
This inner class can be static.
merge MMcM: Add a transaction service API to check for rollback errors at commit whose success state is unknown

Merge pull request #1211 from MMcM/sql-layer/retry-commit-unknown
https://github.com/FoundationDB/sql-layer/pull/1211
merge MMcM: Another backreference due to inner class

Merge pull request #1212 from MMcM/sql-layer/more-query-context-references
https://github.com/FoundationDB/sql-layer/pull/1212