Test case for [OPTIQ-373] NOT IN and NULL values
Inherit maven-release-plugin from Apache POM.
[OPTIQ-343] RelDecorrelator should build its own mappings, not inherit from SqlToRelConverter

Factor out CorrelatorRel.Correlation as a top-level class.

Add SqlExplainLevel.NON_COST_ATTRIBUTES, which includes "id".

Add RelShuttle.visit(CorrelatorRel).