Added _do_dns_lookup_caching class attr to basic user folder.  If this is true.,DNS lookup caching for domain-based restrictions will be performed.  If it's not, DNS lookup caching is bypassed.  It's enabled by default.

Made container and accessed default to aq_parent in _getobcontext.  This was necessary to make the help system work.

stack, to the new DTMLFile.

authentication failure.

- added logic to do domain-defined nobody lookup which I thought I could safely dump before.

- added a hook for ignoring the domain-defined "nobody" lookup, although I'm not going to change the user folder UI right now, and the default behavior of this implementation is the same as the old.

- refactored validate method into identify, authenticate, and authorize methods.

- added _getobcontext method to do acquisition dance to find out accessed, container, and name in order to pass them to securitypolicy.validate

separate function.

POST to the URL of an image already retrieved, it will fetch the image
from its cache and display it rather than submitting the form.  That's
incorrect, but we can work around it.

Not done yet.

Moved Bindings.py (used by DTMLFile), Script.py, and associated files to Shared/DC/Scripts.  Refactored Bindings UI into separate BindingsUI class.
Changed PythonScripts to use DTMLFile.