2) Created ExprNode::expressionEqual method to replace a new big and ugly switch.
3) Make boolean referencers use BoolExprNode instead of jrd_nod, except nod_validate for now. This includes BinaryBoolNode and NotBoolNode working without jrd_nod references.
4) Rework in the impure allocation code (replace "csb_impure += ..." by CMP_impure calls).