TST/FIX ensure correct ducktyping for metaestimators
TST extend ducktype testing to handle #2853 case
FIX ducktyping for meta-estimators
TST more rigorous testing of delegation
remove _iff_attr_has_method function
don't give names to decorators
make attribute decriptor have the right docstring.
add regression test for docstring delegation
fix docstrings in sphinx
rename decorator
Fix typos, no shortenings in name, simplify example.
MAINT: Remove deprecation warnings in enet_path and lasso_path
Merge pull request #4011 from MechCoder/fix_deprecation_paths

MAINT: Remove deprecation warnings in enet_path and lasso_path
Merge pull request #3982 from amueller/metaestimator_delegation

Metaestimator delegation/ducktyping. Fixes #1805.
Fix a bug occurring when n_samples in a class < n_features
Fix case n_sample in a class == 1
warning + log of prod -> sum of log
warning -> error
though we can check if reg_param > 0 and then use spherical covariance,
let's keep things simple
tests
ignore warnings, change docstring
BUG: only symmetrize matrix when it is not already symmetric