Explicitly close all databases on shutdown, which ensures `Data.fs.index` gets written to the file system.

Move Zope2 tests at the end, they tend to leave the process in an unclean state and cause reference couunting / garbage collection timing issues in AccessControl tests

Removed the old help system, in favor of the current Sphinx documentation hosted at http://docs.zope.org/zope2/. For backwards compatibility the `registerHelp` and `registerHelpTitle` methods are still available on the ProductContext used during the `initialize` function.

Removed various persistent product related code and options. The `enable-product-installation` `zope.conf` setting is now a no-op.

Removed the `enable-ms-author-via` directive which was only required for very old web folder implementations from before 2007.

Remove various rarely used options from the example zope.conf.in - they are still present in the zopeschema.xml

Changed zope.conf default settings for `zserver-threads` to `2` and `python-check-interval` to `1000`.

Simplified instance skeleton, removing old `Extensions`, `import`, `lib/python` and `Products` from the default. You can continue to manually add these back.

Removed the rarely used support for the `++skin++` traverser and added instructions on how to get it back for a specific application

Remove duplicated changelog entries for changes also made in 2.13.x - I want to see what's new on trunk

Previously an addAfterCommitHook was used, but this is not run on transaction
aborts.  Now a Synchronizer is used which unconditionally closes the request
after a transaction is finished.

Not closing the request seems to have caused the database connections to be
kept open and these nasty log messages:

    CRITICAL ZODB.DB DB.open() has 42 open connections with a pool_size of 7

42 being the wrong answer in this case.

Make Yvo happy and keep testing our factored out distributions, so CMF doesn't have to grow a KGS of its own