“ The matter was still in the breast of the court; it was free to change its opinion if it saw fit, and it was free to do so by changing the decree without delivering a new opinion to explain what the decree made manifest. If it thought, rightly or wrongly, that the collateral question of the present defendant's liability could not be tried in that case, it properly embodied its decision in the decree. The decree is the dominant act, and cannot be given a greater effect than it purports to have and than would be warranted by the opinion that the court finally reached. ”