A fourth person has been killed this holiday weekend on Missouri Highways. Police say 63-year-old Pamela J. Foster of Liberty was killed this morning (Friday 27) in Clinton County. The car she was riding in went off the roadway and struck a guardrail. Foster was ejected from the vehicle. Three other people have been killed since the holiday weekend started on Wednesday (25) night. Last year, there were 18 deadly crashes in Missouri…