Yes, I don't think Python 2.6 had a deliberate workaround.  I suspect
that it's just that one version of Python happened to use something like
0.0/0.0 to generate NaN, while another used some equivalent of
strtod("nan", ...).

I also remember noticing at some point that even on a single machine/OS,
the sign bit of 0.0/0.0 depends on which version of gcc and which
optimization flags are present.

So I think we're in agreement that there's no need to change anything
here;  I'll close this issue.

But:  I really *would* like to get the short float repr working with
suncc!  Issue #5792 is already open for this, so discussion should move
there.  (This is about much more than consistent nan signs: 
implementing short float repr gives a whole bunch of benefits: correctly
rounded float <-> string conversions (including all float formatting
operations), a correctly rounded 'round' function, a prettier float
repr, ...).