OPENGL_GAL, DrawArcSegment(): do not modify the radius of arc.

The radius correction does not fix correctly approximation errors,
and creates serious issues for thin arcs:
- control point outside the arc
- HitTest active area outside the arc shown on screen
- Cairo and opengl gives different arc positions.
- the formula used in radius correction is probably incorrect.

common/gal/opengl/opengl_gal.cpp

@@ -844,9 +844,17 @@ void OPENGL_GAL::DrawArcSegment( const VECTOR2D& aCenterPoint, double aRadius, d
     // Bigger arcs need smaller alpha increment to make them look smooth
     const double alphaIncrement = std::min( 1e6 / aRadius, 2.0 * M_PI / CIRCLE_POINTS );
 
+    // Code disabled because it creates serious issues:
+    // - The arc is inside the polygonization error, but the interior of arc is also important
+    // and putting error inside the arc creates significant errors inside this arc
+    // - for thin arcs the control points are not even inside the arc, and HitTest is
+    // not even working
+    // I am also pretty sure the formula is incorrect. (JPC)
+#if 0
     // Draw entirely within the real arc boundary (ie: put all polygonization error inside)
     double correctionFactor = cos( M_PI / (double) CIRCLE_POINTS );
     aRadius *= correctionFactor;
+#endif
 
     Save();
     currentManager->Translate( aCenterPoint.x, aCenterPoint.y, 0.0 );