message: Allow bigint to be used as time column in Presto
diff: @@ -832,6 +832,8 @@ class PrestoEngineSpec(BaseEngineSpec):
  return "from_iso8601_date('{}')".format(dttm.isoformat()[:10])
  if tt == 'TIMESTAMP':
  return "from_iso8601_timestamp('{}')".format(dttm.isoformat())
  + if tt == 'BIGINT':
  + return "to_unixtime(from_iso8601_timestamp('{}'))".format(dttm.isoformat())
  return "'{}'".format(dttm.strftime('%Y-%m-%d %H:%M:%S'))
  @classmethod
  