pydata/pandas — pull request #3329 by jreback (2013-04-12 14:40:13+00:00)
Title: PERF/CLN: infer Period in infer_dtype, later index inference is faster

This was meant to fix the vbench: ctor_index_array_string

see #3326

not sure if this is that stable of a perf fix

```
-------------------------------------------------------------------------------
Test name | head[ms] | base[ms] | ratio |
-------------------------------------------------------------------------------
frame_get_dtype_counts | 0.0960 | 0.1700 | 0.5647 |
frame_insert_500_columns | 87.8456 | 142.5257 | 0.6163 |
frame_iteritems_cached | 0.0820 | 0.1043 | 0.7860 |
stat_ops_level_frame_sum | 2.5051 | 2.8849 | 0.8683 |
ctor_index_array_string | 0.0333 | 0.0383 | 0.8693 |
stat_ops_level_series_sum_multiple | 5.6090 | 6.4037 | 0.8759 |
frame_fancy_lookup | 2.7517 | 3.1263 | 0.8802 |
```