Flip the texture coordinates instead of flipping textures.
This simplifies the TextureManager (no need to worry if the caller wants flipping or not), should make it easier to generalize & multithread it.
This means we can more reliably set the filter parameters.
I believe this commit creates a regression where non-DDS GUI textures would display upside down, which will be addressed by further refactoring in the next commits.
For some reason, the mipmap generator seems to be broken on Linux Intel graphics (works on Nvidia). This was breaking the scrollbar arrows, which are minified enough to show using a mipmap.
scrawl