Update plot_svm_regression.py

library imports have been moved to top of the file.
MAINT warn of future behaviour change proposed in #2610
TST/COSMIT tests/comments for [sparse]center_data

Also removes sparse_std which was redundant
DOC: tfidf is actually tf*(idf+1) = tf + tf*idf
COSMIT: More readable drop for good test
FIX: checked in bad assertion in the last commit by mistake
Remove redundant yet unstable test_spectral_lobpcg_mode

The lobpcg mode is already tested in the test_spectral_clustering test.

LinAlgError was raised when executing test_spectral_lobpcg_mode on some
systems depending on the version of the scipy and LAPACK libraries.
TST: more robust test of dropping in Lars
TST: relax warning class checked in lars
TST: lars tests: more brutal ill-conditionning
ENH: make CD Lasso raise ConvergenceWarning
Merge pull request #3030 from ogrisel/fix-lars-drop-for-good-test-failure

Fix LARS drop for good test failure
DOC: clear up the big elastic net confusion (I hope)

Several users have asked for LogReg w/ E-net (e.g. #3023). Did some
additional copyediting.
Merge pull request #3025 from ogrisel/remove-unstable-lobpcg-test

[MRG] Remove redundant yet unstable test_spectral_lobpcg_mode
ENH: stable test + catch warning + pep8
ENH: more robust test_toy_bayesian_ridge_object
ENH: configure travis to also test old numpy & scipy
DOC: add some header doc to the travis scripts
More informative numerical error message in SGD

Also add a test.
cosmit