A Kansas sheriff has pleaded guilty to selling a gun to a convicted felon.     The U.S. attorney’s office says Ness County Sheriff Bryan Whipple entered the plea Monday.  Whipple admits selling a .45 caliber pistol and ammunition to the felon.      As part of the deal, the 48-year-old has agreed to resign and to surrender his law enforcement certification. The prosecution will recommend that he be sentenced to probation. Sent…