[PUSHED][REVIEW-3-5] Fix wrong vcl alpha blending

[Caolán McNamara]

On Tue, 2012-03-27 at 15:31 +0530, Muthu Subramanian K wrote:
> +1
> 
> [There were some duplicate code, which I attempted to remove - if there
> are no mistakes there, pushing that is better? Or probably merging via
> master is better?]

I decided to pick the two commits back to 3-5, presuming that you guys
know what you're doing :-)

C.