Five-localsitemanager

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* More PEP8 compliance.

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* 4: Replace dependency on ZODB3 with persistent, add zope.site.

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* Target use with Zope 4: no longer support 2.13.x.

* Python 3 compatibility

* Added tox test scripts.

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* Don't complain if the site root has no Acquisition parent.
[davisagli]

* Removed zope.site dependency. Using Zope 2.12 it is an indirect dependency
and using Zope 2.13 or later it is no longer required.
[yuppie]

* Ensure that the PersistentComponents has no aquisition wrapper before passing
to the superclass, to allow the caching of component roots in zope.interface
to make a weakref to this root.
[MatthewWilkes]

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* Made the tests compatible with Zope 2.13.2.

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* Deal with deprecation warnings for Zope 2.13.

* Provide a more meaningful error message if the current site is not set
correctly or the Acquisition chain of the site is messed up.
[hannosch]