When a series contains all strings, converting to dtype "int" generates bogus int values
This works:

``` python

In [3]: series = pandas.Series(["car", "house", "tree", 1])

In [4]: series
Out[4]: 
0      car
1    house
2     tree
3        1

In [5]: series.astype("int")
ValueError: invalid literal for long() with base 10: 'tree'
```

This doesn't:

``` python
In [7]: series = pandas.Series(["car", "house", "tree","1"])

In [8]: series.astype("int")
Out[8]: 
0                  0
1           44735616
2    139883221510192
3                  1
```

This with RC2 state from git.
