allow curve shape control points to overlap

diy-layout-creator --username bancika@gmail.com/DIYLC/src/org/diylc/components/AbstractComponent.java

@@ -35,6 +35,11 @@ public abstract class AbstractComponent<T> implements IDIYComponent<T> {
 	public void setName(String name) {
 		this.name = name;
 	}
+	
+	@Override
+	public boolean canControlPointOverlap(int index) {
+		return false;
+	}
 
 	@Override
 	public String toString() {

diy-layout-creator --username bancika@gmail.com/DIYLC/src/org/diylc/components/AbstractCurvedComponent.java

@@ -107,6 +107,12 @@ public abstract class AbstractCurvedComponent<T> extends AbstractTransparentComp
 	public VisibilityPolicy getControlPointVisibilityPolicy(int index) {
 		return VisibilityPolicy.WHEN_SELECTED;
 	}
+	
+	@Override
+	public boolean canControlPointOverlap(int index) {
+		// Only shape control points may overlap.
+		return index == 1 || index == 2;
+	}
 
 	@Override
 	public Point getControlPoint(int index) {