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

line by default to avoid causing problems for proxy servers which do not
correctly handle multi-line headers. (Merged from 2.13 branch.)

The getaddrinfo API provides a superset of the info provided by gethostbyname but isn't ipv4 specific.