MAINT missing import_array() in isotonic r. Cython code

Not extremely important, but issues one less compiler warning.
MAINT get rid of compiler warnings from Liblinear
DOC no more "arithmetical order" for classes
BF: load_boston() return 13 features, but 14 feature names

Last column has the target value, hence only report first 13 names.
Fixes Issue 2751
Merge pull request #2865 from hanke/boston_13features

BF: load_boston() returns 13 features, but 14 feature names
ENH Cache features value for extra trees
FIX: Removed coef and improved initialization
Merge pull request #2866 from Manoj-Kumar-S/Iss2751

Fixes Issue 2751
FIX integer dtype for labels in DBSCAN

Fixes #2833.
FIX numerical stability issue in BernoulliRBM

Fixes #2785 by replacing log1p(exp(x)) with logaddexp(0, x).
Fix typo in fast sgd classifier implementation comments
Merge pull request #2869 from jperla/master

DOC Fix typo in fast sgd classifier implementation comments