Patch-review changes

[David Nolden]

I've fixed all the issues I mentioned now. Porting to a newer version of 
libdiff wasn't such a bad thing, at least we don't depend on Qt3-support any 
more.

But still, this sucked, because I was forced to fix the thing in the end, 
which I kind-of feared right in the moment that I saw you starting to work on 
the plugin.

I think there is something to be learned: If you don't know how something 
works, and especially if you don't even use it, then simply don't touch its 
code! You can only break it then.

Greetings, David