small bug fix to precondition checking for POS3
small bug fix to precondition checking for POS3

digitalreasoning/factorie-scala-210,joprice/factorie,patverga/factorie,pogren-oracle/factorie,malcolmgreaves/factorie,Craigacp/factorie,zxsted/factorie,melisabok/factorie,strubell/factorie,factorie/factorie,hlin117/factorie,asubbaswamy/factorie