pandas.rolling_apply: "Out of bounds on buffer access"
Looks like `pandas.rolling_apply` doesn't like a window larger than the length of the array:

```
In [3]: import pandas

In [4]: import numpy as np

In [5]: a = np.array(range(4))

In [6]: pandas.rolling_sum(a, 10)
Out[6]: array([ nan,  nan,  nan,  nan])

In [7]: pandas.rolling_apply(a, 10, np.sum)
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-7-1ff0414da8bd> in <module>()
----> 1 pandas.rolling_apply(a, 10, np.sum)

/Library/Python/2.7/site-packages/pandas-0.8.1-py2.7-macosx-10.8-intel.egg/pandas/stats/moments.pyc in rolling_apply(arg, window, func, min_periods, freq, time_rule)
    465         return lib.roll_generic(arg, window, minp, func)
    466     return _rolling_moment(arg, window, call_cython, min_periods,
--> 467                            freq=freq, time_rule=time_rule)

/Library/Python/2.7/site-packages/pandas-0.8.1-py2.7-macosx-10.8-intel.egg/pandas/stats/moments.pyc in _rolling_moment(arg, window, func, minp, axis, freq, time_rule, **kwargs)
    227     return_hook, values = _process_data_structure(arg)
    228     # actually calculate the moment. Faster way to do this?
--> 229     result = np.apply_along_axis(calc, axis, values)
    230 
    231     return return_hook(result)

/Library/Python/2.7/site-packages/numpy-1.6.2-py2.7-macosx-10.8-intel.egg/numpy/lib/shape_base.pyc in apply_along_axis(func1d, axis, arr, *args)
     78     outshape = asarray(arr.shape).take(indlist)
     79     i.put(indlist, ind)
---> 80     res = func1d(arr[tuple(i.tolist())],*args)
     81     #  if res is a number, then we have a smaller output array
     82     if isscalar(res):

/Library/Python/2.7/site-packages/pandas-0.8.1-py2.7-macosx-10.8-intel.egg/pandas/stats/moments.pyc in <lambda>(x)
    224     """
    225     arg = _conv_timerule(arg, freq, time_rule)
--> 226     calc = lambda x: func(x, window, minp=minp, **kwargs)
    227     return_hook, values = _process_data_structure(arg)
    228     # actually calculate the moment. Faster way to do this?

/Library/Python/2.7/site-packages/pandas-0.8.1-py2.7-macosx-10.8-intel.egg/pandas/stats/moments.pyc in call_cython(arg, window, minp)
    463     def call_cython(arg, window, minp):
    464         minp = _use_window(minp, window)
--> 465         return lib.roll_generic(arg, window, minp, func)
    466     return _rolling_moment(arg, window, call_cython, min_periods,
    467                            freq=freq, time_rule=time_rule)

/Library/Python/2.7/site-packages/pandas-0.8.1-py2.7-macosx-10.8-intel.egg/pandas/lib.so in pandas.lib.roll_generic (pandas/src/tseries.c:74581)()

IndexError: Out of bounds on buffer access (axis 0)
```
