The segfault is a little worrying;  I don't understand that at all.

Skip, can you come up with a configure patch that would allow isinf to be 
detected on Solaris?

I'll also patch Py_IS_INFINITY to make sure that it forces its argument 
into memory before testing it;  this *should* fix the problem on platforms 
that don't have isinf.  (Note to self:  first find out whether 
Py_IS_INFINITY is ever applied to single precision floats, or whether we 
can assume the argument is always a double.)