Expand Thin Walls is causing slicing errors on retraction performance test

[jlewin]

@unlimitedbacon commented on Wed Jun 06 2018

Make: Printer Benchmark Files
File: 12_retraction_performance_test.stl
Slice using the Pulse C-232 profile with NylonX

I would include pictures but they don't show much. Its better to look at the G-Code view and step through the moves.

Issues

1. Nothing is printed on layer 98
2. On layer 99 and 100 there are double the necessary retractions. Each tower has two retracts instead of one.

I think this is due to expand thin edges not picking up the transition between the lines being found by the normal perimeter code and the need for expansion.

The Other double extrude is tracked in a separate issue.