Insurance Falls Short for Many Workers By THERESA AGOVINO     NEW YORK (AP) -- Privately insured, low-income workers with chronic medical conditions such as diabetes and asthma are being financially squeezed as employers shift the burden of higher health care costs to employees, a new study found.    The number of such individuals spending more than 5 percent of their income on out-of-pocket medical costs soared 48 percent to 2.2 million people from 2001 to 2003, according to a study released Thursday by the Center for Health System Change...