one-entry glx context stack
prune context switching in softVdpPresentationQueueDisplay
use glx_context_push & glx_context_pop
move glx context stack implementation to separate source file
fix signed/unsigned warnings
move VdpDeviceData structure to vdpau-device.h
save XVisualInfo in VdpDeviceData
use different gl contexts per thread
free glx contexts from hash table on vdp device destroy
trace hook which displays current thread id
call trace hook in traceInfo too