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

Thanks to Eric Steele for the patch.

Merged the slinkp-datetime-200007 branch: fix the DateTime(anotherDateTime) constructor to preserve timezones.

traversal.

Merged from branches/slinkp-zopectl-exitcode-143813; fixes # 143813: zopectl should exit non-zero if child processes fail.

'unrestrictedTraverse' (apparent NameError).

Base the default location of softwarehome on Zope2, which is guaranteed not to be a namespace but always located inside the Zope2 software home. This fixes Zope2 breaking on systems which uses namespace packages for Products.*

        caused a LookupError exception. Unknown encodings are from now on
        silently discarded.