Function dt_cook_clause

* Since D permits new variable identifiers to be instantiated in any program * expression, we may need to cook a clause's predicate either before or after * the action list depending on the program code in question. Consider: * * probe-description-list probe-description-list * /x++/ /x == 0/ * { { * trace(x); trace(x++); * } } * * In the left-hand example, the predicate