Slicing non-unique index fails when slice endpoint is not in index
This looks like a regression from 0.13.1. If you have a simple dataframe with a non-unique but sorted index like:

``` python
df = pd.DataFrame(np.arange(5.), index=[datetime(2001, 1, i, 10, 00)
                                        for i in [1,2,2,3,4]])
df
Out[23]: 
                     0
2001-01-01 10:00:00  0
2001-01-02 10:00:00  1
2001-01-02 10:00:00  2
2001-01-03 10:00:00  3
2001-01-04 10:00:00  4

[5 rows x 1 columns]
```

Then in pandas 0.13.1 you could slice a range out of that dataframe with a date not in the index like so:

``` python
# pandas 0.13.1
df.ix[datetime(2001, 1, 2, 11, 0):]
Out[22]: 
                     0
2001-01-03 10:00:00  3
2001-01-04 10:00:00  4

[2 rows x 1 columns]
```

In the HEAD of pandas/master now, you can't. Instead you get a TypeError with long long traceback.

``` python
# pandas 0.14.1
In [58]: df.ix[datetime(2001, 1, 2, 11, 0):]
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-58-c4fe729e46fe> in <module>()
----> 1 df.ix[datetime(2001, 1, 2, 11, 0):]

/users/is/dbew/src/pandas/pandas/core/indexing.py in __getitem__(self, key)
     69             return self._getitem_tuple(key)
     70         else:
---> 71             return self._getitem_axis(key, axis=0)
     72 
     73     def _get_label(self, label, axis=0):

/users/is/dbew/src/pandas/pandas/core/indexing.py in _getitem_axis(self, key, axis, validate_iterable)
    843         labels = self.obj._get_axis(axis)
    844         if isinstance(key, slice):
--> 845             return self._get_slice_axis(key, axis=axis)
    846         elif _is_list_like(key) and not (isinstance(key, tuple) and
    847                                          isinstance(labels, MultiIndex)):

/users/is/dbew/src/pandas/pandas/core/indexing.py in _get_slice_axis(self, slice_obj, axis)
   1090         if not _need_slice(slice_obj):
   1091             return obj
-> 1092         indexer = self._convert_slice_indexer(slice_obj, axis)
   1093 
   1094         if isinstance(indexer, slice):

/users/is/dbew/src/pandas/pandas/core/indexing.py in _convert_slice_indexer(self, key, axis)
    161         # if we are accessing via lowered dim, use the last dim
    162         ax = self.obj._get_axis(min(axis, self.ndim - 1))
--> 163         return ax._convert_slice_indexer(key, typ=self.name)
    164 
    165     def _has_valid_setitem_indexer(self, indexer):

/users/is/dbew/src/pandas/pandas/core/index.py in _convert_slice_indexer(self, key, typ)
    589         else:
    590             try:
--> 591                 indexer = self.slice_indexer(start, stop, step)
    592             except Exception:
    593                 if is_index_slice:

/users/is/dbew/src/pandas/pandas/tseries/index.py in slice_indexer(self, start, end, step)
   1350             raise TypeError('Cannot index datetime64 with float keys')
   1351 
-> 1352         return Index.slice_indexer(self, start, end, step)
   1353 
   1354     def slice_locs(self, start=None, end=None):

/users/is/dbew/src/pandas/pandas/core/index.py in slice_indexer(self, start, end, step)
   1712 
   1713         # loc indexers
-> 1714         return Index(start_slice) & Index(end_slice)
   1715 
   1716     def slice_locs(self, start=None, end=None):

/users/is/dbew/src/pandas/pandas/core/index.py in __new__(cls, data, dtype, copy, name, fastpath, tupleize_cols, **kwargs)
    170                         pass  # python2 - MultiIndex fails on mixed types
    171             # other iterable of some kind
--> 172             subarr = com._asarray_tuplesafe(data, dtype=object)
    173 
    174         if dtype is None:

/users/is/dbew/src/pandas/pandas/core/common.py in _asarray_tuplesafe(values, dtype)
   2106     if not (isinstance(values, (list, tuple))
   2107             or hasattr(values, '__array__')):
-> 2108         values = list(values)
   2109     elif isinstance(values, Index):
   2110         return values.values

TypeError: 'datetime.datetime' object is not iterable
```
