support strings as selectors

example:

  @n: 1;
  ~".span@{n}" { ... }

lib/less/parser.js

@@ -945,6 +945,10 @@ less.Parser = function Parser(env) {
             selector: function () {
                 var sel, e, elements = [], c, match;
 
+                if (sel = $(this.entities.quoted)) {
+                    return new(tree.Selector)([new(tree.Element)('', sel, i)]);
+                }
+
                 while (e = $(this.element)) {
                     c = input.charAt(i);
                     elements.push(e)