Assign boost to GF bit allocation if past frame had no ARF.
Modify the second-pass code to provide a full golden-frame (GF) bit allocation boost if the past GF group (GFG) had no alt-ref frame (ARF), even if the current GFG does contain and ARF. This mostly has no effect on clips, since switching ARFs on/off between GFGs is not very common. Has a positive effect on e.g. cheer (+0.45 SSIM at 600kbps) and football (+0.25 SSIM at 600kbps), particularly at high bitrates. Has a negative effect (-0.04 SSIM at 300kbps) at pamphlet, which appears only marginally related to this patch, and crew (-0.1 SSIM at 700kbps). Change-Id: I2e32899638b59f857e26efeac18a82e0c0b77089