Add check for doomed transactions in default transaction manager, abort silently if the tm tries to commit a doomed transaction

 - Rather nasty fix to work around Zope 3 exceptions that have more than one positional argument on the constructor. Also, pass 'handle_errors' argument used for functional http testing around and use that on raise_standardErrorMessage to decide if we need to care about rendering a full HTML traceback.

  argument/attribute missing in testbrowser tests.

  provided tests and implementation for guarded_zip (RestrictedPython).

- fixed the auth encoding classifier 

 - Add guards for 'all' and 'any', new in Python 2.5. Add support for 'key' keyword argument to 'max' and 'min' guards

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.

 - Avoid raising string exceptions. If one is found, upgrade it to InternalError and keep the original exception name as part of exc_value

  2.6. Adjust tests accordingly.