A note to any potential reviewers for this patch (cmath3.patch):  I'm especially 
looking for non-mathematical feedback here, so please don't be put off by the 
mathematics.  Some questions:

- there's a new file cmath.ctest containing testcases;  should this be put 
directly into Lib/test (where it is right now), or is there a better place.  Is 
the name of this file reasonable?

- is the new stuff in pyport.h (checks for _copysign and copysign, and automatic 
renaming of _copysign to copysign) okay?  Should it be in cmathmodule.c instead?

- is the code in test_cmath that looks for the testcase file okay?

And it would be really great if someone with access to a Windows box could just 
verify that the tests pass with this patch applied;  I've only tested it on OS X 
and Linux.