(Jeremy and Tim) Changed the implementation of ZODB no lon-longer
depend on ExtensionClass.

except that 'Z' is still allowed in front of a '+/-HH:MM' timezone.  I
left that in since it was used elsewhere in the code, and was probably
harmless, whereas the other parse problems caused dates like "2003-2-5"
to be accepted as valid and silently converted into "2003-01-01".

Also re-exposed the DateTime-specific exceptions as attributes of the
DateTime class.  During their recent converted from strings to classes,
they were removed.

     - AccessControl.User used a misleading string exeception,
       'NotImplemented', which shadowed the Python builtin.

Removed support for Python 2.1, fixed yield test, and added a test for
bad names set by exception handlers.

the list of names

Added tests.

throwing OverflowError.

that depends on it to raise an OverflowError when presented with a
number above sys.maxint.  We work around it here.

preferred spelling for 'CONTEXTS/varname'.