Track number of GPU commands executed per call level.

This is to get an idea if it would be beneficial to compile and cache display lists. Looks like it would be for some games, for example in GTA it's often 20k/80k/20k commands per frame - that is 100k executed commands per frame that could potentially just be executed instead of interpreted. Likewise in Wipeout. Of course, this means yet another cache with invalidation issues etc..