Finally after a long discussion on #gedit I reimplemented the whole sourceview plugin in anjuta and reused much of the code from gedit. This is a good idea and a big advantage of open-source software: You can take what you need and don't have to do the same mistakes twice. Thanks to Paolo Borelli and Paolo Maggi for poiting this out!
BTW, it's no real good idea to use Spanish for some comments in gedit :-|
Und es schneit und schneit weiter. Komischer März im Moment !