name and behavior mismatch in pct_change
Hi all,

I've enjoyed using pandas for a little while now. Thanks for developing such a useful and convenient tool!

A little nit has been nagging at me about pct_change function (and the .pct_change method of Series, DataFrame, etc.).  If I run a sequence of numbers that increase by 100% (python 0.16.2):

``` python
import pandas as pd

series = pd.Series([0.5,1,2,4])
print series.pct_change()
```

the output is:

```
0   NaN
1     1
2     1
3     1
dtype: float64
```

Based on the name pct_change, I'd expect the result should the percentage change (i.e., scaled by 100):

```
0   NaN
1     100
2     100
3     100
dtype: float64
```

In general it looks to me like in general pct_change is really a _fractional_ change. Perhaps the name would suggest the behavior more closely if the function and method were called frac_change? I've become familiar with pandas enough now to know the expected behavior, but this could be a confusing turn-off for newer users.
