create python dia plugin : need help !

[lidiriel <lidiriel coriolys org>]

I have recompiled dia 0.95 on linux.
I paste into ~/.dia/python/hello.py , the hello code found in this 
mailling list :
import dia
def hello_callback(data, flags):
  print "Hello, Dia!\n"
dia.register_callback("Hello, world",
                      "<Display>/Plugins/Hello",
                      hello_callback)

my dia is compiled with option --enable-debug and --with-python
But i don't find the plugin entry hello in dia. It the same thing for 
center.py whit a callback function

dia.register_callback ("Center Objects",
                       "<Display>/Objects/Center",
                       dia_objects_center_cb)

What's happended ? I have no idea ?