This was quite a porting mess. The old code would fill up qt/4.4/libraryPath in Trolltech.conf with all kinds of paths, most of them duplicates. This hurt startup time and made applications load plugins from incorrect plugin dirs.

I've rewritten the code to do what it was intended to do:
- look at libraryPath
- remove all entries that KDE added last time
- add all the paths KStandardDirs returns for the qtplugins resource
- store what we added to the list
- store the new list

my libraryPath entry is down from 50 to 1 (after I manually removed all the incorrect paths, which I recommend everybody else to do, too)