There are so many import dependencies between OFS and webdav, it's
otherwise too easy to accidentally cause a cycle and silently break
one module.

Moved to zopefoundation/ZServer@ee3cb3c7576df0de96d0fe96fbdc7912efed3049.

Also adjust some deprecation warnings to refer to Zope 5.0.

Moved to zopefoundation/ZServer@23f8ec7b39c9558bbce83e66b700b8c26693255a.

The locking concept is generally useful and used outside of
the webdav context.

It will be needed by AccessControl 4.0