Fix typo in abstract.c which caused __rpow__ to not be invoked.

Added related testcase.
Closes SF bug #643260.

Lib/test/test_pow.py

@@ -118,3 +118,8 @@ for i in range(-10, 11):
                 o = pow(long(i),j) % k
                 n = pow(long(i),j,k)
                 if o != n: print 'Integer mismatch:', i,j,k
+
+class TestRpow:
+    def __rpow__(self, other):
+        return None
+None ** TestRpow()      # Won't fail when __rpow__ invoked.  SF bug #643260.

Objects/abstract.c

@@ -468,7 +468,7 @@ ternary_op(PyObject *v,
 	if (mv != NULL && NEW_STYLE_NUMBER(v))
 		slotv = NB_TERNOP(mv, op_slot);
 	if (w->ob_type != v->ob_type &&
-	    mv != NULL && NEW_STYLE_NUMBER(w)) {
+	    mw != NULL && NEW_STYLE_NUMBER(w)) {
 		slotw = NB_TERNOP(mw, op_slot);
 		if (slotw == slotv)
 			slotw = NULL;