fix pickle test in Python 3

tests/run/reduce_pickle.pyx

+import sys
+
+if sys.version_info[0] < 3:
+    __doc__ = """
+    >>> import cPickle
+    >>> a = A(5); a
+    A(5)
+    >>> cPickle.loads(cPickle.dumps(a))
+    A(5)
+    
+    >>> b = B(0, 1); b
+    B(x=0, y=1)
+    >>> cPickle.loads(cPickle.dumps(b))
+    B(x=0, y=1)
+    """
+
 cdef class A:
     """
     >>> a = A(3); a
     A(3)
-    >>> import cPickle
-    >>> cPickle.loads(cPickle.dumps(a))
-    A(3)
     >>> import pickle
     >>> pickle.loads(pickle.dumps(a))
     A(3)
@@ -25,9 +38,6 @@ cdef class B:
     """
     >>> b = B(x=37, y=389); b
     B(x=37, y=389)
-    >>> import cPickle
-    >>> cPickle.loads(cPickle.dumps(b))
-    B(x=37, y=389)
     >>> import pickle
     >>> pickle.loads(pickle.dumps(b))
     B(x=37, y=389)