Introduce constructor methods for RelOptRuleOperand: RelOptRule.leaf(), .some(), .any(). This avoids mistakes like only matching a leaf node, where the rule was intended to match a node regardless of its children. The old constructors are deprecated and will be removed soon.
Change signature of createEmptyResultSet; OptiqConnectionImpl isn't public, so method couldn't be called from outside package.
Release 0.4.3.