Fixing #690329: Can't call a Gtk.UIManager.add_ui_from_string() with non-ASCII characters

[Jonathan Ballet <jon multani info>]

Hi,

so, I'm the reporter of
https://bugzilla.gnome.org/show_bug.cgi?id=690329, which I would like to
fix for https://github.com/multani/sonata to work with non-ASCII
playlists.

I gave it a shot today, and found an even simpler test case.
Calling the same function with a string which differs only from one
non-ASCII characters result in the underlying
gtk_ui_manager_add_ui_from_string() called with the same "length"
attribute (containing the same value), whereas, I believe, in the case
where the string passed contains a non-ASCII characters, length should
be bigger.
I attached to the bug report a GDB session which shows this particular
problem.

I made a patch, which seems to fix the problem, at least with my test
case, with both Python 2 and Python 3. I'm struggling a bit to run the
test suite of the repository without resorting to using jhbuild
(./configure dance following with "make check").
I would like to hear from the maintainer what they think about the
problem.

Thanks,

 Jonathan