DatetimeBlock -> FloatBlock in reindex op
```
     floats  ints strings  bools              objects
0 -1.478427     0     foo  False  2000-01-03 00:00:00
1  0.524988     1     bar   True  2000-01-04 00:00:00
2  0.404705     2     foo   True  2000-01-05 00:00:00
3  0.577046     3     bar   True  2000-01-06 00:00:00
4 -1.715002     4     foo  False  2000-01-07 00:00:00
5 -1.039268     5     bar  False  2000-01-10 00:00:00
6 -0.370647     6     foo  False  2000-01-11 00:00:00
7 -1.157892     7     bar  False  2000-01-12 00:00:00
8 -1.344312     8     foo  False  2000-01-13 00:00:00
9  0.844885     9     bar   True  2000-01-14 00:00:00

In [67]: foo.reindex(range(15))
Out[67]:
      floats  ints strings  bools       objects
0  -1.478427     0     foo  False  9.468576e+14
1   0.524988     1     bar   True  9.469440e+14
2   0.404705     2     foo   True  9.470304e+14
3   0.577046     3     bar   True  9.471168e+14
4  -1.715002     4     foo  False  9.472032e+14
5  -1.039268     5     bar  False  9.474624e+14
6  -0.370647     6     foo  False  9.475488e+14
7  -1.157892     7     bar  False  9.476352e+14
8  -1.344312     8     foo  False  9.477216e+14
9   0.844885     9     bar   True  9.478080e+14
10       NaN   NaN     NaN    NaN           NaN
11       NaN   NaN     NaN    NaN           NaN
12       NaN   NaN     NaN    NaN           NaN
13       NaN   NaN     NaN    NaN           NaN
14       NaN   NaN     NaN    NaN           NaN
```
