The most substantial memory leak came from `PacketQueue::get`
not unreferencing its argument packet.
Other leaks came from using `av_free` instead of type-specific free
functions.
Also modifies `PacketQueue::put` for readability.
This should allow OpenMW to work better with git versions of openscenegraph. OSG dev version 3.5.5 added the setting of thread affinity for the main thread. The problem is that in the boost/standard threading libraries, the affinity of a thread is inherited by any further threads launched from that thread, leading to these threads always running on the same core as the main thread unless you tell them not to.
With OpenThreads, the default affinity of a thread is none, no matter what parent thread it was launched from.
So, when using custom threading with OSG 3.6+, we have these options:
1. explicitely tell OSG to *not* set the thread affinity
or 2. explicitely set the thread affinity of additional threads created (possible with boost, but not possible with std::thread)
or 3. use OpenThreads
or 4. accept the suboptimal performance of non-OSG threads (in OpenMW's case the sound streaming & video threads) running on the same core as the main thread
This patch opts for 3.)
Reference: http://forum.openscenegraph.org/viewtopic.php?t=16158
