Natural name convention broken for "size" in non-interactive mode.

If there is a column named "size", the member syntax return the NumPy .size property instead of the contents of the column:

```
$ python -c "import pandas; df=pandas.DataFrame({'size':range(3)}); print df.size; print df['size']"
```

prints

```
3
0    0
1    1
2    2
Name: size, dtype: int64
```
