Better support for multi resolution icon files

Qt supports vector based svg images as icons, which in theory should allow nice icons at all resolutions. In practice where when an icon is displayed at low resolutions it is often necessary to go in by hand and tweak things so that it still looks good.

Because of this it would be nice to be able to use multi resolution rasterized icon containers like .ico and .icns files in funcation calls like setWindowIcon. instead of having to build the QIcons manually each time with QIcon::addFile()
http://doc.trolltech.com/4.4/qicon.html#addFile