Fix implicit coercion of aggregation and window functions
Fix SHOW PARTITIONS

Connectors (such as the Hive connector) that return Slices for their TupleDomains ended up with the
toString() representation of Slice in SHOW PARTITIONS
Fix missing synchronization
Remove redundant (and incorrect) call in IndexManager

This was a left-over from a merge conflict
Merge operator stats atomically
Implement toString for hll
Handle fatal errors in ExchangeClient

Treat certain errors in the HttpPageBufferClient as fatal and abort the
ExchangeClient rather than retrying forever.