PEMBROKE PINES, Fla. – A 15-year-old boy was arrested Thursday after he allegedly made threats against a Broward County high school, authorities said. According to Pembroke Pines police, the boy is a 10th-grade student at South Broward High School in Hollywood and made a threat on Snapchat to “shoot up” Charles W. Flanagan High School in Pembroke Pines…