Memory leak when subsetting and using timeit.Timer
When subsetting a Series object inside of a function that is being run with Python's timeit.Timer module, memory usage grows without bound. Tested with pandas 0.9.1 on Python 2.7.3 32-bit on Windows.

```
from timeit import Timer

def test():
    for i in range(1000000):
        s = pd.Series(np.random.randn(150))
        s[0:100]

t = Timer(lambda: test())
t.timeit(1)
```

If I remove the line s[0:100] the problem disappears.
