Period resampling buglet
```
In [20]: rng = date_range('1/1/2000','12/31/2000')

In [21]: ts = Series(np.random.randn(len(rng)), index=rng)

In [22]: ts.resample('M', kind='period')
Out[22]: 
Jan-2000    0.280017
Feb-2000    0.010740
Mar-2000   -0.175855
Apr-2000   -0.080775
May-2000    0.253388
Jun-2000    0.072629
Jul-2000    0.136193
Aug-2000   -0.039670
Sep-2000   -0.300413
Oct-2000   -0.200501
Nov-2000    0.037753
Dec-2000   -0.053187
Jan-2001         NaN
Freq: M
```
