Fix comparison of types in analysis of UNION
Fix TpchColumnHandle.equals() to compare types correctly
Fix comparison of types in AggregationCompiler
Add CLI program to benchmark a Presto cluster
Include both sources in IndexNode sources list

getSources() is meant to return all subplans of a given node as it's
used for various plan-walking activities.
Implement PlanRewriter as a regular visitor

The rewriter interface abstraction is unnecessary.