For some reason (probably cut and paste), __ipow__ for new-style
classes was called with three arguments.  This makes no sense, there's
no way to pass in the "modulo" 3rd argument as for __pow__, and
classic classes don't do this.  [SF bug 620179]

I don't want to backport this to 2.2.2, because it could break
existing code that has developed a work-around.  Code in 2.2.2 that
wants to use __ipow__ and wants to be forward compatible with 2.3
should be written like this:

  def __ipow__(self, exponent, modulo=None):
      ...
diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index 0c7def1..c9bd1cd 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -3306,6 +3306,16 @@
     vereq(2*a, "rmul")
     vereq(2.2*a, "rmul")
 
+def testipow():
+    # [SF bug 620179]
+    if verbose:
+        print "Testing correct invocation of __ipow__..."
+    class C(object):
+        def __ipow__(self, other):
+            pass
+    a = C()
+    a **= 2
+
 def do_this_first():
     if verbose:
         print "Testing SF bug 551412 ..."
@@ -3401,6 +3411,7 @@
     slottrash()
     slotmultipleinheritance()
     testrmul()
+    testipow()
     if verbose: print "All OK"
 
 if __name__ == "__main__":