MAINT warn of future behaviour change proposed in #2610
MAINT lazily import scipy.cluster

Prevents PIL from being dragged along. Fixes #2961.
ENH micro-optimize a few tests
ENH micro-optimize fast MCD

Tests run 10-20% faster, which is what I was aiming for (it takes
almost 5s on my box).
FIX random_state validation on c_step

Got lost in e6003bc89. Also input validation on X.
DOC mention "shape" in AP docs

http://stackoverflow.com/q/22873622/166749
ENH less copying in validation for neighbors
FIX safe_asarray to handle LIL, DOK formats
TST safe_asarray for dok_matrix and lil_matrix
DOC: website: feature selection on front page

Replaces Isomap. Fixes #3033.
FIX loss function example

The Python API to the loss functions was lost in the last refactor.
Restored the example by defining the losses inline.
Fixed the x-axis to show "f(x)" instead of "y * f(x)".
Removed references to private APIs.
DOC: clustering: merge discussions of k-means and inertia

K-means is hard to understand without knowing what inertia is,
and we still don't have a public function for computing it.
Gets rid of an ugly TODO in the docs.
MAINT remove unsupported documentation formats

In particular, "htmlhelp" and "qthelp". None of the core devs uses
this or is willing to support it. Fixes #2512 by not fixing it.
DOC: move mean_shift docs to MeanShift

The class is linked from the clustering docs, while the function
isn't. Also standardized the spelling on "mean shift". StudlyCaps
version is an artifact of PEP8 class naming.
Merge pull request #2952 from jnothman/future_warn_two_labels

MAINT warn of future behaviour change proposed in #2610
ENH factor out squared norm helper
Now capable of treating sample_weights in feature space
FIX: Set correct impurity values in BestFirstBuilder
PEP8
Merge pull request #3049 from glouppe/tree-bestfirst

[MRG+1] Trees: set correct impurity values in BestFirstBuilder