Motion Blur Bias\Interval Center doesn't work well with multi-frame trails.

[im.thatoneguy]

I'm trying to use motion blur to do long-exposure motion blur trails however there is a small problem with the Bias settings as they're limited to 0.0 to 1.0. So if you are doing a 12 frame motion blur rendering along with a 'head' frame at the head of the streak you have to do a time-offset rendering to align the two.