[NTG-context] followup: arrows in mplib

I'm afraid arrows look better now, but they're not yet quite what they used to be. Test: \setupcolors[state=start] \starttext \startuseMPgraphic{arrowtest} z1=(0,0) ; z2=(3cm,0) ; ahlength := 15pt ; pickup pencircle scaled 5pt ; drawarrow z1--z2 withcolor red ; \stopuseMPgraphic \useMPgraphic{arrowtest} \stoptext Homework for Hans and Taco again? :-) Thomas