BUG: strange behaviour of .index.min()
I was expecting `df.index.min()` here to be equal to `min(df.index)`, and I guess it is; but I wasn't expecting this:

```
>>> import pandas as pd
>>> pd.__version__
'0.13.0-268-g08c1302'
>>> df = pd.DataFrame({"A": [1]})
>>> df.index
Int64Index([0], dtype='int64')
>>> min(df.index)
0
>>> type(min(df.index))
<type 'numpy.int64'>
>>> m = df.index.min()
>>> m == 0
True
>>> type(m)
<class 'pandas.core.index.Int64Index'>
>>> m
[...]
  File "/usr/local/lib/python2.7/dist-packages/pandas-0.13.0_268_g08c1302-py2.7-linux-i686.egg/pandas/core/common.py", line 2570, in as_escaped_unicode
    result = compat.text_type(thing)  # we should try this first
  File "/usr/local/lib/python2.7/dist-packages/pandas-0.13.0_268_g08c1302-py2.7-linux-i686.egg/pandas/core/base.py", line 201, in __unicode__
    quote_strings=True)
  File "/usr/local/lib/python2.7/dist-packages/pandas-0.13.0_268_g08c1302-py2.7-linux-i686.egg/pandas/core/common.py", line 2597, in pprint_thing
    elif _is_sequence(thing) and _nest_lvl < \
  File "/usr/local/lib/python2.7/dist-packages/pandas-0.13.0_268_g08c1302-py2.7-linux-i686.egg/pandas/core/common.py", line 2100, in _is_sequence
    iter(x)
RuntimeError: maximum recursion depth exceeded while calling a Python object
```

The same thing applies to `.max()`.
