test against the new ZK 3.4.6
update bundled virtualenv to 1.11.4
update some testing / docs dependencies
Remove zope.interface dependency, closes #131.
Fixed pipes leaking into child processes, closes #169.
add changelog entry
Allow easier customization of the testing cluster port range, closes #133.
Merge pull request #179 from python-zk/169-fix-pipe-leak

Fixed pipes leaking into child processes, closes #169.
Merge pull request #178 from python-zk/131-remove-zope-interface

Remove zope.interface dependency, closes #131.
Merge pull request #180 from python-zk/133-testing-cluster-ports

Allow easier customization of the testing cluster port range, closes #133
Fix atexit handling for kazoo threading handler.
Merge pull request #183 from wickman/wickman/fix_atexit_nones

Fix atexit handling for kazoo threading handler.
Add changelog for atexit fix to threading handler.