Allow Chain to be frozen, preventing += appends.
Allow Chain to be frozen, preventing += appends.

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