Workaround problems with clip transparency. Transparency is now achieved by inserting...

Workaround problems with clip transparency. Transparency is now achieved by inserting a transition in timeline. This "automatic" transition moves automatically with the clip (at least it tries).
Probably not perfect but I think it is an acceptable workaround for:
http://www.kdenlive.org:80/mantis/view.php?id=220

svn path=/branches/KDE4/; revision=2600