BUG? when incrementing .loc[]-view
Am I doing something wrong with indexing here? 

PS. on the second thought it looks related to #3492, but I don't have a dev environment at hand to test and it fails for some reason when trying to build pandas via pip. If that's the case and it's already fixed, my apologies and feel free to close this one.

Steps to reproduce:

``` python
>>> df = DataFrame(index=np.arange(10))
>>> df['foobar'] = False
>>> df['a'] = np.arange(10)
>>> df
  foobar  a
0  False  0
1  False  1
2  False  2
3  False  3
4  False  4
5  False  5
6  False  6
7  False  7
8  False  8
9  False  9
# This works as expected
>>> df.a[df.a % 2 == 0] += 10
>>> df
  foobar   a
0  False  10
1  False   1
2  False  12
3  False   3
4  False  14
5  False   5
6  False  16
7  False   7
8  False  18
9  False   9
# This doesn't work, but expected due to copying on bool-indexing
>>> df[df.a % 2 == 0].a += 100
>>> df
  foobar   a
0  False  10
1  False   1
2  False  12
3  False   3
4  False  14
5  False   5
6  False  16
7  False   7
8  False  18
9  False   9
# But what does this?
>>> df.loc[df.a % 2 == 0, 'a'] += 1000
>>> df
  foobar     a
0  False  1010
1  False     1
2  False  1010
3  False     3
4  False  1010
5  False     5
6  False  1010
7  False     7
8  False  1010
9  False     9

>>> pandas.__version__
'0.11.0'
```
