SF #660455 : patch by NNorwitz.

"Unsigned" (i.e., positive-looking, but really negative) hex/oct
constants with a leading minus sign are once again properly negated.
The micro-optimization for negated numeric constants did the wrong
thing for such hex/oct constants.  The patch avoids the optimization
for all hex/oct constants.

This needs to be backported to Python 2.2!