Mouse over detection on cricle, arc, locus

[hilaire]

The Cuis's VectorGraphics engine detects points colision with those lines as filled surface. DrGeo needs detecting only the perimeter line.

Add the appropriate methods for these circle, arc and locus morph so colision is done only with the line, not the surface.

[hilaire (hilaire-fernandes)]

For those morphs that can't rely on the VectorGraphics detection method with pixel, we use the math model and closestPointTo: method for proximity detection.