hub/changefeed: similar to 9e4653663631a73ddc4c692d239767e3face551c also prevent new_val_update from running if already closed -- e.g. query in handle_change takes too long (?)
hub/changefeed: similar to 9e4653663631a73ddc4c692d239767e3face551c also prevent new_val_update from running if already closed -- e.g. query in handle_change takes too long (?)

DrXyzzy/smc,tscholl2/smc,DrXyzzy/smc,sagemathinc/smc,sagemathinc/smc,sagemathinc/smc,tscholl2/smc,sagemathinc/smc,tscholl2/smc,DrXyzzy/smc,tscholl2/smc,DrXyzzy/smc,tscholl2/smc