Ftw.testing

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- Nothing changed yet.

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- Significantly optimize freezer's "ignore_modules" by avoiding retrieving the
complete call stack.
[buchi]

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- Stop quickinstall_uninstallation test from being skipped on Plone 5.1 [djowett-ftw]
- restore diffs for uninstall tests after removing unittest2 [djowett-ftw]

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- Add missing getToolByName default argument [Nachtalb]

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- Fix pickling of datetime while time is frozen. [buchi]

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- Fix super call to mock_tool. [buchi]