remove EJSON.clone of data context in urlFor, pathFor and linkTo

Note, we still clone individual attributes. But for the main data
context we'll just create a new object and merge into it. That we we're
assigning new properties to the new object vs. mutating the original
data context. But we'll avoid the circular reference loops that cause
problems for EJSON.clone.

lib/helpers.js

@@ -37,7 +37,7 @@ UI.registerHelper('pathFor', function (options) {
   var query = opts.query;
   var hash = opts.hash;
   var routeName = routeName || opts.route;
-  var data = EJSON.clone(opts.data || this);
+  var data = _.extend({}, opts.data || this);
 
   var route = Router.routes[routeName];
   warn(route, "pathFor couldn't find a route named " + JSON.stringify(routeName));
@@ -78,7 +78,7 @@ UI.registerHelper('urlFor', function (options) {
   var query = opts.query;
   var hash = opts.hash;
   var routeName = routeName || opts.route;
-  var data = EJSON.clone(opts.data || this);
+  var data = _.extend({}, opts.data || this);
 
   var route = Router.routes[routeName];
   warn(route, "urlFor couldn't find a route named " + JSON.stringify(routeName));
@@ -120,7 +120,7 @@ UI.registerHelper('linkTo', new Blaze.Template('linkTo', function () {
   var query = opts.query;
   var hash = opts.hash;
   var routeName = opts.route;
-  var data = EJSON.clone(opts.data || DynamicTemplate.getParentDataContext(this));
+  var data = _.extend({}, opts.data || DynamicTemplate.getParentDataContext(this));
   var route = Router.routes[routeName];
   var paramKeys;