Update: An additional comment from James A. White was added to the third-to-last paragraph.A corrections officer’s testimony justifying the alleged actions of Cook County jail officials — who are being sued for violating an inmate’s civil rights — is not admissible, a federal judge has ruled.Two lawsuits against Cook County Sheriff Thomas J. Dart and several sheriff’s officials claim the office habitually used excessive force toward inmate Reginald Potts Jr.The proposed expert, Martin Horn …