* Add whatever X-DBUS-foo line KUniqueApplication says we need.
* Restructure the startup sequence to postpone all the hard work until after the GUI is setup
  as much as possible to allow passing our reply over DBUS ASAP.
* Don't call hasCover from PlaylistItem like, ever.  I made CoverInfo::hasCover() take longer
  when I added support for APIC frames but didn't catch all unnecessary instances of their use
  last time.  Luckily this is the big win and is backportable.
* Also, don't force CoverInfo::coverId() to call hasCover() for no reason.

Hopefully this should remove the egregrious Plasma freeze-ups while starting but even after
returning from KUniqueApplication::newInstance() quickly it seems to take a while for the reply
to go over the D-BUS...

svn path=/trunk/KDE/kdemultimedia/juk/; revision=851610