Adding column of floats to DataFrame yields TypeError
I have a function that builds a DataFrame of summary statistics that I have used routinely for several months, but now breaks due to a change in Pandas over the past few weeks. Specifically, I have the following list of floats:

```
(Pdb) [r[0] for r in ratios]
[1.1200000000000001, 5.0, 0.73999999999999999, 0.35999999999999999,  
1.1100000000000001, 1.1699999999999999, 0.92000000000000004,  0.94999999999999996, 1.0600000000000001, 0.77000000000000002,  
0.59999999999999998, 2.0099999999999998, 3.2999999999999998, 0.37,  
1.6100000000000001, 1.02]
```

Which I use to create a column in the following table:

```
(Pdb) table
oxygen                0     1
male               0.57  0.59
under 2 months     0.06  0.23
2-11 months        0.66  0.59
12-23 months       0.23  0.10
Jordanian          0.90  0.91
Palestinian        0.05  0.06
vitamin D < 20     0.55  0.53
vitamin D < 11     0.40  0.38
prev_cond          0.11  0.11
heart_hx           0.05  0.04
breastfed          0.68  0.56
premature          0.13  0.23
adm_pneumo         0.09  0.25
adm_bronchopneumo  0.52  0.28
adm_sepsis         0.11  0.16
adm_bronchiolitis  0.21  0.21
```

However, this now causes the following:

```
(Pdb) table['foo'] = [r[0] for r in ratios]
*** TypeError: Not implemented for this type
```

Here is a more verbose output:

```
TypeError                                 Traceback (most recent call last)
<ipython-input-49-0723b2a631c0> in <module>()
----> 1 make_table(groupby_o2, table_vars=table_vars, replace_dict={0.0: 'No Oxygen', 1.0: 'Oxygen'})

<ipython-input-47-6f3ebc37c721> in make_table(groupby, table_vars, replace_dict)
      3     ratios = [calc_or(groupby, v) for v in table.index]
      4     import pdb; pdb.set_trace()
----> 5     table['OR'] = [r[0] for r in ratios]
      6     table['Interval'] = [r[1] for r in ratios]
      7     table['N'] = [r[2] for r in ratios]

/usr/local/lib/python2.7/site-packages/pandas/core/frame.pyc in __setitem__(self, key, value)
   1899         else:
   1900             # set column
-> 1901             self._set_item(key, value)
   1902 
   1903     def _setitem_slice(self, key, value):

/usr/local/lib/python2.7/site-packages/pandas/core/frame.pyc in _set_item(self, key, value)
   1982         self._ensure_valid_index(value)
   1983         value = self._sanitize_column(key, value)
-> 1984         NDFrame._set_item(self, key, value)
   1985 
   1986         # check if we are modifying a copy

/usr/local/lib/python2.7/site-packages/pandas/core/generic.pyc in _set_item(self, key, value)
   1137 
   1138     def _set_item(self, key, value):
-> 1139         self._data.set(key, value)
   1140         self._clear_item_cache()
   1141 

/usr/local/lib/python2.7/site-packages/pandas/core/internals.pyc in set(self, item, value, check)
   2637 
   2638         try:
-> 2639             loc = self.items.get_loc(item)
   2640         except KeyError:
   2641             # This item wasn't present, just insert at end

/usr/local/lib/python2.7/site-packages/pandas/core/index.pyc in get_loc(self, key)
   2055 
   2056     def get_loc(self, key):
-> 2057         if np.isnan(key):
   2058             try:
   2059                 return self._nan_idxs.item()

TypeError: Not implemented for this type
```

Not exactly sure which change caused it, but this code was working on the same data 3-4 weeks ago.

Currently running 0.13.1-936-g592a537 on OS X 10.9.3, Python 2.7.6 from Homebrew.
