commit
For testing the new iteration, the texture cache disk download was written
into the main thread instead of into the separate threads. Now they're back
in separate threads again.
Also I think some of these files probably should have been in the previous
commit.
specific code
The new rendering system is now starting to work as planned, however it is
still not as complete as the iteration before. But this should be a more
robust design moving forward. Work was also done towards splitting off all
OpenGL-specific worker code into a derived class. The hope is to have no
hard dependency on OpenGL and make swapping it out with other backends
straight-forward.