Fully implement Hash Join

Defect Tracker #24376: Based upon the old com.metamatrix.query.processor.relational.HashJoinStrategy (now deleted, but can be resurrectedfrom cvs) fully implement the hash join feature. Costing should be used in RuleChooseJoinStrategy to look for situations in which merge joins are valid but that have one side that is much smaller than the other (and preferable smaller than a processing batch).