Code of Criminal Procedure, 1973–Sec. 439(2)–Cancellation of bail–Scope for–Held, very cogent and overwhelming circumstances are necessary for an order directing the cancellation of bail already granted–Bail once granted, should not be canceled in a mechanical manner without considering whether any supervening circumstances have rendered it no longer conducive to a fair trial to allow accused to retain his freedom by enjoying concession of bail during the trial.