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I am back at work after finishing my move so I think I can
finally devote a little more time to this issue.

1-4) The main reason for datetimeapi.h as opposed to simply
modifying datetime.h was that the internal build needs to
define things __differently__ from an external build of a
module and there doesn't appear to be any way of fixing that
-- so if you know a way I think I can manage to create a
reasonable patch; otherwise, I'm out of my depth!

5) Guido was suggesting that a new PyIMPORT macro be made
available which would verify that the magic number defined
in the header file actually matches the magic number
exported by the built module; this is simply a developer
protection scheme which should eliminate really stupid uses;
you can ask him about this or I can e-mail you part of the
thread that brought this up

6) Makes sense. I'd like to get the questions above resolved
first before proceeding any further, though.