ENH: add PolynomialFeatures preprocessor
address PR2585 comments
import pylab -> import matplotlib.pyplot
TST: fix PolynomialFeatures test error
TST: fix doctests & pep8
DOC: adjust notes in PolynomialFeatures
reorder polynomial features
fix ordering & docs of PolynomialFeatures
TST: remove stray print statement
ENH: ElasticNetCV and LassoCV raise ValueError with multitarget outputs
DOC: multiclass: make the warning more prominent

Too many newbies are asking questions involving a
OneVsRestClassifier(LinearSVC()) or similar construct
on the various forums.
DOC improve feature selection docs
COSMIT remove useless "if False" in kernel approximations

Callable case handled by pairwise_kernels.
FIX regression in CountVectorizer handling of float min_df/max_df

Fixes #2595.
BF: use hasattr with providing attr name (Thanks to Timo Schulz)
BUG: fix partial_fit of MiniBatchDictLearning

The inner state of the algorithm (essentially sufficient statistics
approximating the data already seen) were not kept, and as a result
partial_fit was strongly sub-optimal
DOC: update whats_new
DOC explain ARPACK algorithm in TruncatedSVD docstring

Fixes #2572.
DOC: typo in kernel formulas
Merge pull request #2608 from jakevdp/master

DOC: typo in kernel formulas