BF: explicitly mark train_test_split as not the one for nosetesting

otherwise nose might consider running it resulting in
  File "/tmp/buildd/scikit-learn-0.13/debian/python-sklearn/usr/lib/python2.7/dist-packages/sklearn/cross_validation.py", line 1349, in train_test_split
    raise ValueError("At least one array required as input")
ValueError: At least one array required as input

as was also reported on the mailing list
Message-ID: <50F6B2D3.1010801@sina.com>
TST stronger tests for arbitrary classes. make explicit what works and what doesn't.
BUG allow outlier_label=0 in RadiusNeighborClassifier

Fixes #1602.
BUG in RadiusNeighborClassifier outlier handling

Ruggedized the test, which wasn't doing much previously, and added a test
for c0d4015d201b68e5da6afe4c7fb8b0e6819f038c.

Also replaced flatten (which copies) with ravel and improved the error
message for outliers in the face of outlier_label=None.
ENH rewrite radius-NN classifier's outlier handling

Fixes a bug introduced in 2dfe13d0a7c0c482961ad49ae04b89bdc81f9d00.
IMHO, the code is much more readable this way.
ENH set the random state to avoid heisenfailures
COSMIT pep8
DOC some copyediting
REL increased version number, added whatsnew
sponsor update by NelleVaroquaux
Merge pull request #1916 from jaquesgrobler/sponsors_update

sponsor update by NelleVaroquaux
update paypal buttons to 0.13 website
no newline fix
Merge pull request #2149 from jaquesgrobler/Donate_Buttons_stable_build

update paypal buttons to 0.13 website
FIX: Cast floats to int before slicing in robust_covariance

Fixes #1608.
BUG fix failing doctests
add loss function for gradient boosting binomial deviance
correct docstring
remove the equaldistance code warning, replace with doc warnings
COSMIT remove unused imports, pep8