message: impala support for epoch timestamps
diff: @@ -1425,6 +1425,10 @@ class ImpalaEngineSpec(BaseEngineSpec):
  Grain('year', _('year'), "TRUNC({col}, 'YYYY')", 'P1Y'),
  )
  + @classmethod
  + def epoch_to_dttm(cls):
  + return 'from_unixtime({col})'
  +
  @classmethod
  def convert_dttm(cls, target_type, dttm):
  tt = target_type.upper()
  