On a sunny Sunday afternoon, just before the final week of classes at Boston University, Parissa Salimian is taking a break from hours of studying for finals, staring bleary-eyed at passersby from her perch atop the steps just outside the entrance of Mugar Memorial Library. She’s smoking a filtered Camel cigarette, joining about a dozen smokers who have stepped outside to light up in order to cope with the pressures of preparing for exams and writing final papers. >>