rolling_* with min_periods=0
I ran into a minor gotcha with the rolling_\* methods, below is some ipython output to illustrate.
I set min_periods to 0, which in retrospect i realize is not a reasonable value, but i would either 
expect the same behavior as min_periods=1 or maybe an error.  For rolling_max, the issue is
with line 421 in moments.pyx:
 "for i from minp - 1 <= i < N:"
so if minp==0 then the first value of i = -1, which will wreak all kinds of havoc.   

In [10]: df
Out[10]: 
   0 
0  7 
1  9 
2  8 
3  20

In [11]: pandas.rolling_max(df,window=df.shape[0],min_periods=0)
Out[11]: 
   0 
0  20
1  20
2  20
3  20

In [12]: pandas.rolling_max(df,window=df.shape[0],min_periods=1)
Out[12]: 
   0 
0  7 
1  9 
2  9 
3  20
