Grok

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- Directly depend on zope.app.wsgi and configure it too to have the useful
IResult adapters for (temporary) files registered.

- Import grokcore.component.global_adapter too.

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- Fix tests that relied on older versions of zope.testbrowser.

- Added grok.index.Value component.

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- Added import for Subscription and MultiSubscription components.

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- Fix tests now that error views no longer by default provide ISystemErrorView.

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- Should've listed IApplication as part of the grok API too.

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- Grok should still provide IApplication in the grok API, even now that it
got moved to grokcore.site.interfaces.