Fix #703, traces are now just lines but they're much faster!

Bugfix for https://github.com/elm-lang/Elm/issues/703

This is a visual change as well:
Original:
![screen shot 2014-07-24 at 2 24 10 pm](https://cloud.githubusercontent.com/assets/1889997/3689820/5c4f14fe-1343-11e4-8245-07972d57f167.png)

Bugfix:
![screen shot 2014-07-24 at 5 02 48 pm](https://cloud.githubusercontent.com/assets/1889997/3689848/a3307ac0-1343-11e4-8e9a-4a6fc97cce0d.png)