Drop support for Python 2.6.

Make PyContainedProxyBase inherit directly from AbstractPyProxyBase. 

Add tox environments for testing ZODB integration and ZODB integration in pure-python mode; run one of these environments on Travis. This reveals a bug in the new ContainedProxy object: it must be weakly referencable to go in the picklecache, so make that possible.

Make zope.proxy and persistent direct dependencies since we import from them, and pin them to the versions we need for pure-python operation.

Inherit directly from PyProxyBase. This should fix the same problems mentioned in zopefoundation/zope.proxy#5, plus reduce redundant code.

[ci skip]

[ci skip]

[ci skip]

Downloaded from http://downloads.buildout.org/2/bootstrap.py