Implementation of logistic_regression_path.

This is mostly the code from Gael's logistic_cv branch. My work is only some
minor cleanup some added tests and benchmarking.
Take into account @agramfort's comments.

Only cosmetic changes.
Some fixes for LogisticCV object
Docstring of LogisticRegressionCV
Docstring
Refactor and some bug fixing
Docstring
FIX missing import
FIX: bug in LogisticRegressionCV
Make tests deterministic
FIX: coef.shape
Just to be sure
Add test
BUG when fit_intercept=False
Fallback for failing line search
Remove warning (not needed any more)
Compatibility for old scipy
iterate some more on line search
cosmetic
FIX: Tests, LogisticRegressionCV cannot handle multilabel classes now