Incorrect truncating of Series according to max_rows
Series is not correctly truncated according to the max_rows (number of rows is halved).

```
In [146]: s = pd.Series(np.random.randn(20))

In [147]: pd.options.display.max_rows = 10

In [148]: s
Out[148]:
0    1.545202
1   -1.427565
2   -0.961094
...
17    0.125228
18    2.153724
19   -0.384024
Length: 20, dtype: float64

In [149]: s.to_frame()
Out[149]:
           0
0   1.545202
1  -1.427565
2  -0.961094
3   0.387392
4   1.036472
..       ...
15  0.918433
16 -0.874253
17  0.125228
18  2.153724
19 -0.384024

[20 rows x 1 columns]
```
