DOC add note about joblib hashing
DOC add note about joblib hashing

and default pickle protocol in CHANGES.rst

aabadie/joblib,joblib/joblib,aabadie/joblib,tomMoral/joblib,tomMoral/joblib,karandesai-96/joblib,lesteve/joblib,karandesai-96/joblib,joblib/joblib,lesteve/joblib