Z3c.traverser

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- Adapt to the move of IDefaultViewName from zope.component to zope.publisher.

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- Make ``PluggableBrowserTraverser`` implement ``IBrowserPublisher``
interface.
- Fix tests and deprecation warnings.
- Improve test coverage.
- Get rid of zope.app.zapi dependency by replacing its uses with direct
calls.
- Change package's mailing list address to zope-dev at zope.org,
because zope3-dev at zope.org is now retired.
- Change "cheeseshop" to "pypi" in the package's url.

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- Bugfix: In z3c.traverser.stackinfo the traversal stack got messed up
when using the VirtualHost namespace with more than one thread.

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- Restructuring: Separated pluggable traverser functionality into two classes
for better code reuse.

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- Bugfix: if viewlet and managers get nested a viewlet was not found if
the depth reaches 3 because the context was set to the page and not
to the context object.

- Bugfix: replaced call to ``_getContextName`` because it has been removed
from ``absoluteURL``.

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- Update package meta-data.

- Resolve ``ZopeSecurityPolicy`` deprecation warning.