DataFrame.get_value() doesn't work with no unique monotonic MultiIndex
Here is the test code:

```
import pandas as pd
from numpy.random import randint

midx = pd.MultiIndex.from_arrays([randint(0, 3, 20), randint(10, 13, 20)]).order()
df = pd.DataFrame({"x":randint(0, 100, 20)}, index=midx)

df.get_value((1, 10), "x")
```

It seems that the `values.searchsorted()` failed in  `_get_loc_duplicates()` in index.pyx.

Currently, I use following code to get the value:

```
class Loc(object):
    def __init__(self, loc):
        self.loc = loc

    def __cmp__(self, other):
        return cmp(self.loc, other)

df.get_value(Loc((1, 10)), "x")    
```
