added dict_archive; moved db_archive to sql_archive; require sqlalchemy;
enable storing serialized objects in sql_archive; moved archive_dict to cache;
added __len__ and __contains__ methods to archives; added test_alchemy.py
NOTE: *dead_code* activated when sqlalchemy not found, supports sqlite only


git-svn-id: svn+ssh://svn.mystic.cacr.caltech.edu/pathos/klepto@558 8bfda07e-5b16-0410-ab1d-fd04ec2748df
Merge branch 'master' of https://github.com/uqfoundation/klepto