Waterline fix

In the general edge-push function there was a guard against horizontal edges, since they are supposed to be handled by a special horizontalEdgePush() function. But there was no check for vertical edges. They are special too, and caused the rather strange looking behavior with BallCutter seen below.


With BullCutter the code stopped at an assert() and there was no toolpath output at all.

This is now hopefully fixed and we simply give up and return in generalEdgePush() if we encounter a horizontal or a vertical edge. These should be handled upstream by simpler specialized functions. Never assume general position is the take home message I guess...