“It may in some cases be fair and just to make such an order even though the defendant is, himself, counterclaiming, but I am persuaded that it would be wrong to do so, because the costs that these defendants are incurring to defend themselves may equally and perhaps preferably be regarded as costs necessary to prosecute their counterclaim. The fact that the plaintiffs are plaintiffs and the defendants are counterclaiming defendant instead of the other way round appears on the facts here to be very largely a matter of chance.”