Replace messy tests with cleaned-up versions from trunk.

o This move breaks an import cycle in third-party code which avoids imports
  from 'Globals.'
  
o Leave the class importable from its old location without deprecation.

- 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.

into CVS trunk 8 years ago..

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

HTTP spec (RFC 2616).

  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.