Danbury City Council President Joe Cavo underwent unplanned heart bypass surgery yesterday.  He is recovering at Bridgeport Hospital.  Mayor Mark Boughton says Cavo planned to have the procedure at some point, but it was moved up after he fell ill this week.  Council Majority Leader Vinny DiGilio will be interim council president and lead Monday's proposed budget public hearing.  Boughton told the Newstimes that Cavo could return as soon as the May meeting, when the Council will vote on the budget.  Monday's hearing is at 7pm.  Cavo was first elected to the City Council in 2003 and has served as president since 2006.