for making Zope 2.12 run with ZODB 3.9 (having ZopeUndo removed)

  however is still available on the Python level.

- No longer show the Help! links in the ZMI, if there is no help available. The help system depends on the product registry.

- Updated the quick start page and simplified the standard content. The default index_html is now a page template.

- Removed deprecated Draft and Version support from Products.OFSP. Also removed version handling from the control panel. Versions are no longer supported on the ZODB level.

- Removed left-overs of the deprecated persistent product distribution mechanism.

Give the ProductFolder back its type restriction. After ZClasses are gone, you cannot manage those TTW anymore. Automatic creation as part of the startup process still works.

The persistent product registry is not required for starting Zope anymore. `enable-product-installation` can be set to off if you don't rely on the functionality provided by the registry.

Seems some of these functions have persistent references to them in a standard install, so we better leave them in place.

ZClasses have been deprecated for two major releases. They have been removed in this version of Zope.

Python has deprecated the message attribute of exceptions in 2.6. We will keep it for this exception and avoid the warning, as message has a special meaning here.

Avoid deprecation warnings for the md5 and sha modules in Python 2.6 by adding conditional imports for the hashlib module.

o Also, weak "without_version_txt" test to use non-existing filename, rather
  than the (existing) Zope2 directory.

Fix the busted 'aqlegacy_ftest' doctests, by ensuring that the dummy Implicit view base class doesn't acquire 'index_html'.

o Replaced  imports from the 'Globals' module throughout the tree with
  imports from the actual modules;  the 'Globals' module was always intended
  to be an area for shared data, rather than a "facade" for imports.

o Added 'zope.deferredimport.deprecation' entries to 'Globals/__init__.py'
  for all previously imported symbols / modules.

o Moved 'ApplicationdefaultPermissions' from 'App/class_init.py' to
  'AccessCoontrol/Permission.py', to avoid possible import cycle in
  third-party code.

o Moved canonical location of UNIQUE / REPLACEABLE / NOT_REPLACEABLE
  constants from 'Globals' to 'OFS.ObjectManager'.

o Removed 'stuffGlobals' hack in favor of the deferred / deprecation
  imports.

Reverse searching order; start with the presumably smaller specific set and work our way up to larger and larger docid sets. This makes intersecting faster for most common index distributions.

- The level < 0 case is basically the union of all searches for levels 0 through to max. Just call search() for each level and use multiunion on all the results.
- Shorten the 'no-such-path' detection to one test.

Obviously the level < 0 case has been implemented before the index was merged into CVS trunk 8 years ago..

Fix one fragile doctest, band-aid another.

'tal:on_error' handler has attributes visible to restricted code.