Bring back private UIDs for Color.

SVG Export for multiple gradients was broken.

src/path/CurveLocation.js

@@ -47,7 +47,7 @@ var CurveLocation = Base.extend(/** @lends CurveLocation# */{
         // NOTE: We do not use the same pool as the rest of the library here,
         // since this is only required to be unique at runtime among other
         // CurveLocation objects.
-        this._id = CurveLocation._id = (CurveLocation._id || 0) + 1;
+        this._id = UID.get(CurveLocation);
         this._curve = curve;
         // Also store references to segment1 and segment2, in case path
         // splitting / dividing is going to happen, in which case the segments

src/style/Color.js

@@ -605,6 +605,9 @@ var Color = Base.extend(new function() {
             }
             // Default fallbacks: rgb, black
             this._type = type || 'rgb';
+            // Define this Color's unique id in its own private id pool.
+            // NOTE: This is required by SVG Export code!
+            this._id = UID.get(Color);
             if (!components) {
                 // Produce a components array now, and parse values. Even if no
                 // values are defined, parsers are still called to produce

src/util/UID.js

@@ -17,6 +17,7 @@
  */
 var UID = {
     _id: 1,
+    _pools: {},
 
     /**
      * Returns the next unique id.
@@ -24,7 +25,17 @@ var UID = {
      * @return {Number} The next unique id
      * @static
      **/
-    get: function() {
-        return this._id++;
+    get: function(ctor) {
+        if (ctor) {
+            // Use one UID pool per given constructor
+            var name = ctor._class,
+                pool = this._pools[name];
+            if (!pool)
+                pool = this._pools[name] = { _id: 1 };
+            return pool._id++;
+        } else {
+            // Use the global UID pool:
+            return this._id++;
+        }
     }
 };