DialogLineprops in backend_gtk3 calling libglade

Hello

While working on my multi-figure-backend I found an error in DialogLineprops

If you transform the example
matplotlib/examples/user_interfaces/lineprops_dialog_gtk.py
to use the Gtk3 backend you get with a nice error

Traceback (most recent call last):
  File "/home/fariza/workspace/matplotlib/examples/user_interfaces/lineprops_dialog_gtk.py",
line 21, in <module>
    dlg = DialogLineprops([l1,l2])
  File "/home/fariza/workspace/matplotlib/lib/matplotlib/backends/backend_gtk3.py",
line 711, in __init__
    import Gtk.glade
ImportError: No module named Gtk.glade

The current implementation of backend_gtk3 requires libglade for DialogLineprops
but if I am not wrong libglade is being replaced by Gtk.Builder.

If the solution is to move to Gtk.Builder
The transition involves creating a new glade file and reworking
DialogLineprops to use the new api.

Just for my information,
When was this DialogLineprops in Gtk3 introduced?
I just want to know if I can rework it to accept figures instead of
lines, to be compatible with my multi-figure-backend.
Or if it has a large userbase and needs to be updated as it is.

Thanks
Federico

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--
Y yo que culpa tengo de que ellas se crean todo lo que yo les digo?

-- Antonio Alducin --