MAINT use CBLAS instead of Fortran API in Liblinear

This saves code and lets Liblinear benefit from fast BLAS implementations
(ATLAS, OpenBLAS, MKL).
fix issue #2901
Merge pull request #2981 from matrixorz/master

fix issue #2901
TST skip `test_k_means_plus_plus_init_2_jobs` on Mac OS X 10.9. See GH-636
TST fix sklearn.ensemble.tests.test_bagging.test_parallel

n_jobs variable was unused previously, leaving n_jobs=-1 case untested for BaggingRegressor.
TST move Mac OS checking utility to sklearn.utils.testing
TST skip SparsePCA n_jobs!=1 test on Mac OS X because it hangs
adding test for csr data for partial fit
pep8-ing
PY3 file handling
BUG restore joblib logging behavior

.write is not the same as print: the former doesn't append a '\n'.
BUG joblib writes to wrong dir

Sorry, I should have reviewed #2978 more carefully.
DOC trees/ensembles: class labels need not be integers
Add space to be consistent with _tree.pyx
DOC document internal tree class
ENH rename CONSTANT_FEATURE_THRESHOLD to FEATURE_THRESHOLD + revert some pep8 fix for readability
DOC missing words
Merge pull request #2977 from arjoly/tree-cleanup

[MRG] Some cleanup in _tree.pyx
removing copy() and adding tests for multiple forms of sparse matrices
removing tests for multiple sparse matrix formats