As city officials prepare for the Democratic National Convention in July, Boston commuters have gotten used to increased security on public transit. So news that security could be tightened even more in response to a new terrorism warning didn’t faze most residents, who accepted it as a necessity after the 2001 terrorist attacks. “If it can help make us a whole lot safer, the inconvenience is worth it,” said Queen Owens, a 44-year-old Boston medical assistant. “After Sept. 11, I think we should all be worried a little bit. What’s to prevent a surprise from really happening again?” Full Story