bug [ 1175022 ] property example code error

Doc/lib/libfuncs.tex

@@ -755,6 +755,7 @@ class C:
 
 \begin{verbatim}
 class C(object):
+    def __init__(self): self.__x = None
     def getx(self): return self.__x
     def setx(self, value): self.__x = value
     def delx(self): del self.__x