setup-pyrex.py works with 0.9.7.2

Greg fixed the latest bug that caused PySoy to raise a dict assignment error on import with 0.9.7.

Pyrex 0.9.7.2 was released a few hours ago with this fix, and I've updated setup-pyrex.py to work with either 0.9.6.4 or >=0.9.7.2.

Beta-3 is still blocked by the multicore race condition caused by redundant incref/decref calls on Python arguments to class methods in this latest version of Pyrex.