History for samples

changed:
-The AtomicExecution contextmanager will handle all the calls to set_atomic() for you.  Here's the code:
The AtomicExecution contextmanager will handle all the calls to set_atomic() for you.  Since this is just a direct translation of the code on http://zope.stackless.com/wiki/Tasklets , it should work correctly.

Here's the code:

added:
    from __future__ import with_statement