The assistant Principal of the middle school that became the center of a national uproar when about 25 students were denied lunch has been suspended and demoted.   Current Attleboro and incoming New Bedford Public Schools Superintendent Pia Durkin announced that Coelho Middle School assistant principal Susan Fortin has been suspended for 5 days and when she returns to work she will be reassigned as a teacher.   The students were denied lunch earlier this month by workers for the school system's meals contractor because they could either not afford to pay or their pre-paid accounts were depleted.  The company has since fired four employees.  The Sun Chronicle reports that Durkin said Fortin was overseeing lunch that day and did not question the decision by the workers to deny the students lunch.