BUG: Preserve tz of start_date in Holiday.dates

Previously, the timezone of only the start_date was lost, causing the
subsequent call to `DatetimeIndex` to fail if a both start_date and
end_date were tz-aware.

Author: ssanderson

pandas/tseries/holiday.py

@@ -203,7 +203,10 @@ def dates(self, start_date, end_date, return_name=False):
         end_date = Timestamp(end_date)
 
         year_offset = DateOffset(years=1)
-        base_date = Timestamp(datetime(start_date.year, self.month, self.day))
+        base_date = Timestamp(
+            datetime(start_date.year, self.month, self.day),
+            tz=start_date.tz,
+        )
         dates = DatetimeIndex(start=base_date, end=end_date, freq=year_offset)
         holiday_dates = self._apply_rule(dates)
         if self.days_of_week is not None: