Some cleanup and provide an explicit test_suite function, the automatic discovery and ZopeTestCase don't seem to like each other

Added a new API ``get_packages_to_initialize`` to ``OFS.metaconfigure``. This replaces any direct access to ``Products._packages_to_initialize``. The OFS.Application.install_package function takes care of removing entries from this list now.

notify IDatabaseOpenedWithRoot

test also for IDatabaseOpened

Added a new API to ``OFS.metaconfigure.get_registered_packages`` which replaces any direct access to ``Products._registered_packages``.

Changed product install so it won't write persistent changes only to abort them. Instead we don't make any database changes in the first place.

Directly extend and use the Zope Toolkit KGS release 1.0dev-r113891 from http://download.zope.org/zopetoolkit/index/. We should get a proper alpha release in time.

Also makes the intent clearer.

Changed the default for ``enable-product-installation`` to off. This matches the default behavior of buildout installs via plone.recipe.zope2instance.

- LP #597594: Performance optimization in OFS.subscriber.maybeWarnDeprecated.