[cosmetics] renamed "addon" parameters to "client" to better reflect
the actual meaning
[pvr] actually use the PVR_CLIENT typedef
[pvr] use const iterator whenever possible
[pvr] add IsStopping() and IsStopped methods
[pvr] actually use the state helper methods
[pvr] make the state helper methods inline
[pvr] reuse some code by adding a QueueJob() method