Merge pull request #19 from dukhlov/master

Small fix of storage impl default value
Merge pull request #20 from dukhlov/master

Small fixes
Cassandra backend: delete item 'where'
Cassandra backend: delete item 'if'
Tests disabled since driver does not support conditional updates
Merge pull request #21 from ikhudoshyn/cassandra-crud-for-items

Cassandra crud for items
Allow new features with tox v1.6
Reasons:
 - tox update v1.6
Changes:
 - tox 1.6 allows us to skip the sdist step, which is slow.
 - It also allows us to override the install line. In this case, it's
   important as it allows us to stop getting pre-release software we
   weren't asking for.

Original patch by Monty Taylor, talked about here:
http://lists.openstack.org/pipermail/openstack-dev/2013-September/015495.html
Cassandra backend: select item
Cassandra backend: select item with conditions on indexed fields
Added 'system_hash' field
Merge pull request #24 from ikhudoshyn/cassandra-select-item

Cassandra select item
Merge pull request #23 from denismakogon/tox16

Allow new features with tox v1.6