Make Ember.HTMLBars version of registerHelper private.

Author: rwjblue

packages/ember-htmlbars/lib/helpers.js

@@ -19,8 +19,8 @@ var helpers = o_create(null);
 import Helper from "ember-htmlbars/system/helper";
 
 /**
-  @public
-  @method registerHelper
+  @private
+  @method _registerHelper
   @for Ember.HTMLBars
   @param {String} name
   @param {Object|Function} helperFunc the helper function to add

packages/ember-htmlbars/lib/main.js

@@ -68,8 +68,7 @@ registerHelper('unbound', unboundHelper);
 
 if (Ember.FEATURES.isEnabled('ember-htmlbars')) {
   Ember.HTMLBars = {
-    helpers: helpers,
-    registerHelper: registerHelper,
+    _registerHelper: registerHelper,
     template: template,
     compile: compile,
     precompile: precompile,