Issue Description:

In one file I have:

class LineGraphic {
  func intersectionWithLine(g: LineGraphic, extended: Bool = false) {...}
}

In another I have:

class ConstructionLine: LineGraphic {
  func intersectionWithLine(g: LineGraphic, extended: Bool = true) {...}
}

When I call for an intersection on a ConstructionLine without an explicit extended parameter the value of extended is false instead of defaulting to true. In this instance I don't know if the line I am call intersection on is a regular line or a construction line.

I suspect that if I upcast the line to a construction line it will get the default value of extended right, but it seems like it should do so anyway. This is probably a result of this being a compiler generated default, rather than a runtime determined value, but the latter could be accomplished by creating two entry points for the actual function, one with the parameter and one without that assigns the correct default.