Datetime

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- Fixed mapping of EDT (was -> 'GMT-0400', now 'GMT-4').

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- Added EDT timezone support. Addresses bug 599856.
[vangheem]

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- Launchpad 572715: Relaxed pin on pytz, after applying a patch from
Marius Gedminus which fixes the apparent API breakage.

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- Removed an undeclared testing dependency on zope.testing.doctest in favor of
the standard libraries doctest module.

- Added a maximum version requirement on pytz <= 2010b. Later versions produce
test failures related to timezone changes.

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- Launchpad 290254: Forward-ported fix for '_micros'-less pickles from
the Zope 2.11 branch version.

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- Include *all* pytz zone names, not just "common" ones.

- Fix one fragile doctest, band-aid another.

- Fix for launchpad 267545: DateTime(DateTime()) should preserve the
correct hour.