ATHENS (Reuters) - Greece narrowed its central government budget deficit, excluding local authority and social security spending, by 37 percent in the first nine months of 2012, the finance ministry said on Thursday, but revenues were still off target. Spending cuts reduced the budget gap to 12.6 billion euros ($16.3 billion) from 20.1 billion in the same period last year. The figures exclude key elements of the general government budget, which is the one used by the European Union to assess Greece's fiscal performance under an EU/IMF bailout program. ...