tests and implementation for guarded_zip (RestrictedPython).

for failed imports, obscuring later attempts to import the same broken module.

'AccessControl.ZopeGuards.guarded_import' mapped some Unauthorized exceptions
onto ImportErrors:  don't do that!  Also, removed mutable defaults from
argument list, improved tests.

  when editing a page template through the ZMI

the PreferredCharset resolver now deals with situations
where 'context' has no REQUEST attribute

        Timezones() returns a copy of the timezone list (allows tests to run).
        (Backport of r89373 from trunk).

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o That module needs to use Z2-style interfaces in 2.11, for BBB, but
  the Interface module itself issues the warning on import.

        for sending a mail immediately by-passing the zope.sendmail delivery
        mechanism

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o Issue deprecation warning on import of the Interface package). That package
  is already gone on the trunk.