Clearing frees resources, closing also sends out the end-request event. Clones
of the current request need to be cleared, only the actual current request
needs to be closed. Fixes LP #414757.

systems

Moved zope.security-style permission registrations from Products.Five into the AccessControl package.

Cleaned up outdated documentation in reStructuredText and removed import checks, since we can now rely on the dependency declaration in our setup.py.