upstream imports r1067

eihrul (10):
      transformbb factoring
      use aamask to limit region of avatar shadow bias
      distbias aamask fix
      addz usage
      basic pitchcorrect setup
      use C_base as pitch target
      use native symbols for OpenGL 1.3 on Linux
      textureOffset is still buggy on texture rectangles with mesa
      workaround for loading screen bug on mesa
use loopstart and loopend for loopvshaderparams