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Neal, thanks for the additional encouragement. The issues
I'm worried about with regard to signed/unsigned are on the
user code side. In most cases it's a signed format string
matching to an unsigned variable, and often is for a
positive only value (count or length, or similar).

I doubt more than a couple python programs try to use values
large enough for it to be relevant (outside of semantically
questionable -1 markers), however before arbitrarily
changing format strings, I want to be sure such a -1 value
parsed with an unsigned format string will not start raising
ValueErrors - I want my patch to be a candidate for
backporting if desired. Better to leave well enough alone if
it's mostly safe.

There are also tons of unsigned char * variables passed for
string formats; since I don't know why they are explicitly
unsigned, and most of Python works as is, I'd rather just
leave those alone. It would suck to hit one of the special
cases for which it really needs to be an unsigned char *.