add option to mangle names even if eval/with is in use

(for more fair comparison to Closure compiler)

lib/utils.js

@@ -247,16 +247,30 @@ function makePredicate(words) {
 
 function Dictionary() {
     this._values = Object.create(null);
+    this._size = 0;
 };
 Dictionary.prototype = {
-    set: function(key, val) { return this._values["$" + key] = val, this },
+    set: function(key, val) {
+        if (!this.has(key)) ++this._size;
+        this._values["$" + key] = val;
+        return this;
+    },
     get: function(key) { return this._values["$" + key] },
-    del: function(key) { return delete this._values["$" + key], this },
+    del: function(key) {
+        if (this.has(key)) {
+            --this._size;
+            delete this._values["$" + key];
+        }
+        return this;
+    },
     has: function(key) { return ("$" + key) in this._values },
     each: function(f) {
         for (var i in this._values)
             f(this._values[i], i.substr(1));
     },
+    size: function() {
+        return this._size;
+    },
     map: function(f) {
         var ret = [];
         for (var i in this._values)