“On the one hand, the claim cannot simply say, like Mr Micawber, that some gaping hole in its case may be remedied by something which may turn up on disclosure. The claimant must demonstrate that it has a case which is unsuitable to be determined adversely to it without a trial. On the other, the court cannot ignore reasonable grounds which may be disclosed at the summary judgment stage for believing that a fuller investigation of the facts may add to or alter the evidence relevant to the issue …”