rent power" to revoke bail when necessary to insure the defendant's appear- ance ' or to protect the integrity o he judi- cial process. See, e.g., Carbo United States, 82 S.Ct. 662, 667-69, 7 L. .2d 769 (Douglas, Circuit Justice) (prof tion of witnesses) (1962); Fernandez United Page 8 States,