v0.14 group.head() not really grouped
This might not necessarily a new thing since 0.14, but I find the output of group.head() not appropriate for a grouping:

``` python
df = pd.DataFrame(np.random.randn(6,2))
df['A'] = [1,2,2,1,1,2]
df
```

```
          0         1  A
0 -0.047101  0.828542  1
1  1.617815  0.362700  2
2  1.366453 -1.116897  2
3  0.086743 -0.611371  1
4  1.918440 -1.230909  1
5 -1.003828 -0.592541  2
```

``` python
g = df.groupby('A')
g.head(2)
```

```
          0         1  A
0 -0.047101  0.828542  1
1  1.617815  0.362700  2
2  1.366453 -1.116897  2
3  0.086743 -0.611371  1
```

My expectation of the previous output would be:

```
          0         1  A
0 -0.047101  0.828542  1
3  0.086743 -0.611371  1
1  1.617815  0.362700  2
2  1.366453 -1.116897  2
```

because, after all, this is the result of a grouping, so things should be displayed grouped, shouldn't they?
