MultiIndex reindex should behave like Index.
xref #10347 

I'm having trouble understand how exactly reindex is supposed to work in the case of MultiIndex.  What I would like is the exact behavior in the Index case where values can be filled or padded according to some level of the MultiIndex.  I can't understand what reindex is doing in the MultiIndex case.  The below is an example where I would like to interpolate using the prior value a month frame to an hourly frame.

```
import pandas as pd
d1 = pd.date_range('1/1/2012', '3/1/2012', freq='MS')
df = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6]}, index=d1)
dfu = df.unstack()

dfu
Out[12]: 
A  2012-01-01    1
   2012-02-01    2
   2012-03-01    3
B  2012-01-01    4
   2012-02-01    5
   2012-03-01    6
dtype: int64

d2 = pd.date_range('1/1/2012', '3/31/2012', freq='D')

dfu.reindex(d2, level=1) # What is this supposed to do?
Out[17]: 
A  2012-01-01    1
   2012-02-01    2
   2012-03-01    3
B  2012-01-01    4
   2012-02-01    5
   2012-03-01    6
dtype: int64

df.reindex(d2, method='pad').unstack() #Ideally something like this, but without the trickery
Out[19]: 
A  2012-01-01    1
   2012-01-02    1
   2012-01-03    1
   2012-01-04    1
   2012-01-05    1
   2012-01-06    1
   2012-01-07    1
   2012-01-08    1
   2012-01-09    1
   2012-01-10    1
   2012-01-11    1
   2012-01-12    1
   2012-01-13    1
   2012-01-14    1
   2012-01-15    1
...
B  2012-03-17    6
   2012-03-18    6
   2012-03-19    6
   2012-03-20    6
   2012-03-21    6
   2012-03-22    6
   2012-03-23    6
   2012-03-24    6
   2012-03-25    6
   2012-03-26    6
   2012-03-27    6
   2012-03-28    6
   2012-03-29    6
   2012-03-30    6
   2012-03-31    6
Length: 182, dtype: int64
```
