BUG: reindex by both index and columns loses DatetimeIndex frequency
Given:

```
from numpy import ones
from pandas import DataFrame, __version__
df = DataFrame(ones((3, 3)), index=[datetime(2012, 1, 1), datetime(2012, 1, 2), datetime(2012, 1, 3)], columns=['a', 'b', 'c'])

time_freq = date_range('2012-01-01', '2012-01-03', freq='d')
some_cols = ['a', 'b']
```

We get:

```
__version__
```

> '0.10.1'

```
df.reindex(index=time_freq).index.freq
```

> &lt;1 Day&gt;

```
df.reindex(index=time_freq, columns=some_cols).index.freq
```

> None

```
df.reindex(index=time_freq).reindex(columns=some_cols).index.freq
```

> &lt;1 Day&gt;
