Sort by column but keep index
I find myself using DataFrames a lot for obvious reasons but not using the indexing magics all the time. I can get by fine with an integer index a la numpy. This leads to situations where I have to do things like this quite often

``` python
df = df.drop(drop_idx)
df.index = pandas.Index(range(len(df)))
```

or 

``` python
df.sort(columns='col1', inplace=True)
df.index = pandas.Index(range(len(df)))
```

Might be nice to have some sort of keyword in these situations to either reset the index or keep the index unless there's a better way. I always read the docs for reset_index too to see that I'm not missing this functionality there. Don't have time to look into this now but just thought I'd float the idea.
