HDFStore casting all numeric columns to datetime
I will update with a self contained example if I manage to find one (please tell me if necessary).

```
print df.dtypes
0              int64
1              int64
2             object
3             object
4             object
5             object
6     datetime64[ns]
7            float64
8              int64
9              int64
10             int64
11           float64
12           float64
13              bool
14              bool
15             int64
16            object
17             int64
18             int64
19             int64
20             int64
21             int64
22             int64
23           float64
24           float64
25           float64
26           float64
27           float64
28           float64
29           float64
30           float64
31           float64
32           float64
33           float64
34           float64
35           float64
36           float64
37           float64
38           float64
39           float64
40           float64
41           float64
42           float64
43           float64
44           float64
45           float64
46           float64
47           float64
48           float64
49             int64
50             int64
51           float64
52           float64
53             int64
Length: 54

store = HDFStore('data.h5')
store['last_three_months'] = df
store.close()

store = HDFStore('data.h5')
test = store['last_three_months']
print test.dtypes

0     datetime64[ns]
1     datetime64[ns]
2             object
3             object
4             object
5             object
6     datetime64[ns]
7     datetime64[ns]
8     datetime64[ns]
9     datetime64[ns]
10    datetime64[ns]
11    datetime64[ns]
12    datetime64[ns]
13    datetime64[ns]
14    datetime64[ns]
15    datetime64[ns]
16            object
17    datetime64[ns]
18    datetime64[ns]
19    datetime64[ns]
20    datetime64[ns]
21    datetime64[ns]
22    datetime64[ns]
23    datetime64[ns]
24    datetime64[ns]
25    datetime64[ns]
26    datetime64[ns]
27    datetime64[ns]
28    datetime64[ns]
29    datetime64[ns]
30    datetime64[ns]
31    datetime64[ns]
32    datetime64[ns]
33    datetime64[ns]
34    datetime64[ns]
35    datetime64[ns]
36    datetime64[ns]
37    datetime64[ns]
38    datetime64[ns]
39    datetime64[ns]
40    datetime64[ns]
41    datetime64[ns]
42    datetime64[ns]
43    datetime64[ns]
44    datetime64[ns]
45    datetime64[ns]
46    datetime64[ns]
47    datetime64[ns]
48    datetime64[ns]
49    datetime64[ns]
50    datetime64[ns]
51    datetime64[ns]
52    datetime64[ns]
53    datetime64[ns]
Length: 54
```
