DST raw pointers - *-pointers are fat pointers

r? @pnkfelix or @nikomatsakis 
I don't think it can because our `macro_rules` does not allow for optional trailing commas.  Or at least, you do not get them automatically with `$(...),*`, and I do not know if you can express them otherwise.  The last time I tried to emulate the effect in `macro_rules!` i was not successful.