Please describe the problem:
Some Python plugins, such as select objects by color or gtkconsole, don't get 
added to the user interface even though they call filter_register_callback.  
Specifically, plugins that add themselves to the toolbox menubar are added 
correctly, but plugins that add themselves elsewhere, such as to the display 
menubar, are not.  

Steps to reproduce:
1.  Compile from CVS, using --with-python when you ./configure.
2.  Start Dia and verify that Python support has been built correctly by 
looking for a python objects item under the help -> Self Documentation entry of 
the toolbox menubar.
3.  Click on the objects menu of the main display menubar.  Look for a "Select 
by Color" entry, or select anything by color (one of the python plugins offers 
three such choices).  You won't see any.
4.  Alter the register_callbacks line of one of the missing python modules to 
add it to the toolbox menubar in the same way that the pydiadoc module does, 
and restart Dia.
5.  The module you altered should now have a menu entry under the toolbox 
menubar, even though it wouldn't show up in other locations.

Actual results:


Expected results:


Does this happen every time?
Yes.

Other information:
HB says:

BTW: This isn't at all PyDia specific, it just happens that PyDia is
the only user of filter_register_callback() and apprently the menu bar
does not correctly handle filter_get_callbacks().