Introduce performance trace functionality
Rewrite code to avoid VC++ deprecation warnings
Instrument some seekbar and cache functions
Erase window background to the background color
Add args support to trace
Instrument GDI frontend
Remove SetPixelV madness from GDI frontend
Tweak downmix code
Bump version to 0.2.39.4
Merge branch 'release/0.2.39.4' into develop