Evaluate function calls properly.

- `fun(f())` is now possible
- Anonymous can take normal strings
- Tests for `%()`

lib/less/tree/anonymous.js

@@ -1,7 +1,7 @@
 if (typeof(require) !== 'undefined') { var tree = require('less/tree') }
 
 tree.Anonymous = function Anonymous(string) {
-    this.value = string.content;
+    this.value = string.content || string;
 };
 tree.Anonymous.prototype = {
     toCSS: function () {

lib/less/tree/call.js

@@ -8,10 +8,8 @@ tree.Call = function Call(name, args) {
     this.args = args;
 };
 tree.Call.prototype = {
-    eval: function (env) { return this },
-
     //
-    // When generating CSS from a function call,
+    // When evaluating a function call,
     // we either find the function in `tree.functions` [1],
     // in which case we call it, passing the  evaluated arguments,
     // or we simply print it out as it appeared originally [2].
@@ -22,14 +20,20 @@ tree.Call.prototype = {
     // we try to pass a variable to a function, like: `saturate(@color)`.
     // The function should receive the value, not the variable.
     //
-    toCSS: function (context, env) {
-        var args = this.args.map(function (a) { return a.eval(context) });
+    eval: function (env) {
+        if (this._value) return this._value;
+
+        var args = this.args.map(function (a) { return a.eval(env) });
 
         if (this.name in tree.functions) { // 1.
-            return tree.functions[this.name].apply(tree.functions, args).toCSS();
+            return this._value = tree.functions[this.name].apply(tree.functions, args);
         } else { // 2.
-            return this.name +
-                   "(" + args.map(function (a) { return a.toCSS() }).join(', ') + ")";
+            return this._value = new(tree.Anonymous)(this.name +
+                   "(" + args.map(function (a) { return a.toCSS() }).join(', ') + ")");
         }
+    },
+
+    toCSS: function (env) {
+        return this.eval(env).toCSS();
     }
 };