Define #clone() for various Gradient classes. Needs testing.

src/color/Gradient.js

@@ -24,6 +24,13 @@ var Gradient = this.Gradient = Base.extend({
 		this.type = type || 'linear';
 	},
 
+	clone: function() {
+		var stops = [];
+		for (var i = 0, l = this._stops.length; i < l; i++)
+			stops[i] = this._stops[i].clone();
+		return new Gradient(stops, this.type);
+	},
+
 	getStops: function() {
 		return this._stops;
 	},

src/color/GradientColor.js

@@ -25,6 +25,11 @@ var GradientColor = this.GradientColor = Color.extend({
 			this.setHilite(hilite);
 	},
 
+	clone: function() {
+		return new GradientColor(thisgradient, this._origin, this._destination,
+				this._hilite);
+	},
+
 	getOrigin: function() {
 		return this._origin;
 	},

src/color/GradientStop.js

@@ -34,6 +34,10 @@ var GradientStop = this.GradientStop = Base.extend({
 		}
 	},
 
+	clone: function() {
+		return new GradientStop(this._color.clone(), this._rampPoint);
+	},
+
 	getRampPoint: function() {
 		return this._rampPoint;
 	},