Zope-schema

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- Rename the validation token, used in the validation of schema with Object
Field to avoid infinite recursion:
``__schema_being_validated`` became ``_v_schema_being_validated``,
a volatile attribute, to avoid persistency and therefore,
read/write conflicts.

- Don't allow "[\]^`" in DottedName.
https://bugs.launchpad.net/zope.schema/+bug/191236

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- Improve error messages when term tokens or values are duplicates.

- Fix the buildout so the tests run.

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- fix validation of schema with Object Field that specify Interface schema.

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- Prefer the standard libraries doctest module to the one from zope.testing.

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- Avoid maximum recursion when validating Object field that points to cycles

- Make the dependency on ``zope.i18nmessageid`` optional.

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- Allow "setup.py test" to run at least a subset of the tests runnable
via ``bin/test`` (227 for ``setup.py test`` vs. 258. for
``bin/test``)

- Make ``zope.schema._bootstrapfields.ValidatedProperty`` descriptor
work under Jython.

- Make "setup.py test" tests pass on Jython.