broken timestamp asvs
@mroeschke do these indicate incorrectly written benchmarks?

```
asv continuous -f 1.1 -E virtualenv master HEAD -b timeseries -b timestamp -b timedelta -b period -b offset
[...]
[  1.86%] ··· Running gil.nogil_datetime_fields.time_period_to_datetime                          failed
[  2.13%] ··· Running indexing.AssignTimeseriesIndex.time_frame_assign_timeseries_index          failed
[...]
[ 45.48%] ··· Running timestamp.TimestampProperties.time_dayofweek                               failed
[ 45.74%] ··· Running timestamp.TimestampProperties.time_dayofyear                               failed
[ 46.01%] ··· Running timestamp.TimestampProperties.time_days_in_month                           failed
[ 46.28%] ··· Running timestamp.TimestampProperties.time_freqstr                                 failed
[ 46.54%] ··· Running timestamp.TimestampProperties.time_is_leap_year                            failed
[ 46.81%] ··· Running timestamp.TimestampProperties.time_is_month_end                            failed
[ 47.07%] ··· Running timestamp.TimestampProperties.time_is_month_start                          failed
[ 47.34%] ··· Running timestamp.TimestampProperties.time_is_quarter_end                          failed
[ 47.61%] ··· Running timestamp.TimestampProperties.time_is_quarter_start                        failed
[ 47.87%] ··· Running timestamp.TimestampProperties.time_is_year_end                             failed
[ 48.14%] ··· Running timestamp.TimestampProperties.time_is_year_start                           failed
[ 48.40%] ··· Running timestamp.TimestampProperties.time_microsecond                             failed
[ 48.67%] ··· Running timestamp.TimestampProperties.time_offset                                  failed
[ 48.94%] ··· Running timestamp.TimestampProperties.time_quarter                                 failed
[ 49.20%] ··· Running timestamp.TimestampProperties.time_tz                                      failed
[ 49.47%] ··· Running timestamp.TimestampProperties.time_week                                    failed
[ 49.73%] ··· Running timestamp.TimestampProperties.time_weekday_name                            failed
```