Pass env with toCSS in function call evaluation; Add tests; Fixes less#957

Author: dmcass

lib/less/tree/call.js

@@ -36,7 +36,7 @@ tree.Call.prototype = {
             }
         } else { // 2.
             return new(tree.Anonymous)(this.name +
-                   "(" + args.map(function (a) { return a.toCSS() }).join(', ') + ")");
+                   "(" + args.map(function (a) { return a.toCSS(env) }).join(', ') + ")");
         }
     },
 

test/css/functions.css

@@ -4,6 +4,7 @@
   height: undefined("self");
   border-width: 5;
   variable: 11;
+  background: linear-gradient(#000000, #ffffff);
 }
 #built-in {
   escaped: -Some::weird(#thing, y);

test/less/functions.less

@@ -1,10 +1,12 @@
 #functions {
   @var: 10;
+  @colors: #000, #fff;
   color: _color("evil red"); // #660000
   width: increment(15);
   height: undefined("self");
   border-width: add(2, 3);
   variable: increment(@var);
+  background: linear-gradient(@colors);
 }
 
 #built-in {