The draw_lines method in the PS backend divides the line
> into subsequences of at most 50 points, and calls the
> "stroke" operator for each subsequence, which in effect
> resets the dash offset. Thus if 50 consecutive points fit
> within a dash, the line appears solid.
50 seems awfully small to me. There are maximum length path
limitations of some postscript interpreters which is why we batch
these up. Darren, could we get away with a step of 1000 here rather