CategoricalDomain: fixing possible data race found by thread sanitizer
CategoricalDomain: fixing possible data race found by thread sanitizer

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