reset the content root when it's a dir in case we go from single file to a directory package

svn path=/trunk/KDE/kdelibs/; revision=974597

private/packages.cpp

@@ -188,6 +188,7 @@ void WallpaperPackage::pathChanged()
     QFileInfo info(path());
 
     if (info.isDir()) {
+        setContentsPrefix("contents/");
         findBestPaper();
     } else {
         // dirty trick to support having a file passed in instead of a directory