A sickening substance sprayed at a recent pro-Palestinian protest at Columbia University smelled like “raw sewage and decaying carcass” and compelled several demonstrators to seek medical attention, students and faculty told the Daily News. Six people who attended Friday’s on-campus protest reported exposure to a stink bomb or other type of gas, according to police. Students felt their eyes burn and experienced severe symptoms including nausea and migraines, they told The News and wrote on social media. The incident came during the latest in a series of heated demonstrations in the city since …