[PD] More pdp blues

[Yves Degoyon]

>
> this fix also removes the effect of remanence you could see in the 
> canvas :
> previous packets were still displayed
> although they should have disappeared from the system.
> now, this effect has gone and maybe you really wanted it.
> in that case, you have to simulate this by using pdp_reg objects.

i made a new fix that keeps that remanence effect now,
so, forget that remark.

cheers,
sevy