Products-cmfquickinstallertool

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- Updated the delete portalobjects method to NOT delete items that implement
IContentish or IFolderish. This will help people who create custom products
and put content containers at the root on install
[eleddy]

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- Use the new get_registered_packages API in Zope 2.13+ to get the registered
packages, instead of the _registered_packages attribute of the Products
module.
[davisagli]

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- Uninstall control panels.
[elro]

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- Use the standard libraries doctest module.
[hannosch]

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- Reworked the last bits of the install machinery to work without the product
registry.
[hannosch]

- Refactored common code to check and generate the external install methods into
helper methods in utils.
[hannosch]

- Freed listInstallableProducts from its dependency on the product registry.
[hannosch]

- Added a get_packages helper methods to reduce the dependencies on the
persistent product registry and convert the getProductFile method to use it.
[hannosch]

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- Limit the installable products screen to listing only extension profiles
which are either registered without a `for` attribute (i.e. for any type
of context), or registered for `Products.CMFCore.interfaces.ISiteRoot` or
`Products.CMFPlone.interfaces.IPloneSiteRoot`. This allows products to
use another marker interface to group profiles together, without fear of
those showing up in `portal_quickinstaller`.
[optilude]