BUG: resample().asfreq() looses end period with TimedeltaIndex
```
In [16]: df=pd.DataFrame(data=[1,3], index=[dt.timedelta(), dt.timedelta(minutes=3)])
In [17]: df
Out[17]:
          0
00:00:00  1
00:03:00  3

In [18]: df.resample('1T').mean()
Out[18]:
            0
00:00:00  1.0
00:01:00  NaN
00:02:00  NaN
00:03:00  3.0

In [19]: df.resample('1T').asfreq()
Out[19]:
            0
00:00:00  1.0
00:01:00  NaN
00:02:00  NaN
```

The two examples should give the same result. 
Tried it with a DatetimeIndex, and there I don't see this problem.

cc @jreback 
