BUG: scatter_matrix draws incorrect axis
Closes #5662. Refactored a little.

Made examples to confirm 1st and 2nd row's yaxis are identical.

```
import pandas as pd
import numpy as np
df = pd.DataFrame(np.random.randn(100, 3))
df[0] = df[1]
pd.tools.plotting.scatter_matrix(df)
```

![figure_1](https://cloud.githubusercontent.com/assets/1696302/6092365/63f4ce98-af1e-11e4-9175-eba45b483bba.png)

```
df[1] = df[1] / 3 - 2
df[0] = df[1]
pd.tools.plotting.scatter_matrix(df)
```

![figure_2](https://cloud.githubusercontent.com/assets/1696302/6092366/68041dea-af1e-11e4-8ecd-cfcb33aaf1a9.png)
