A U.S. Supreme Court ruled that sentencing juvenile offenders to life in prison is unconstitutional without considering the child's life circumstances.   As a result of the precedent, hundreds of young offenders in Pennsylvania have had their sentences reviewed.  The Miller v. Alabama case is a major guiding force within the Keystone College Juvenile Justice Institute which opened last fall.   Its goals are to help children avoid involvement with the juvenile justice system, to offer alternatives to those already involved,  and to help the incarcerated return to society.