Provide clear throw on {{#each}}

Fixes #773

lib/handlebars/base.js

@@ -97,10 +97,8 @@ function registerDefaultHelpers(instance) {
   });
 
   instance.registerHelper('each', function(context, options) {
-    // Allow for {{#each}}
     if (!options) {
-      options = context;
-      context = this;
+      throw new Exception('Must pass iterator to #each');
     }
 
     var fn = options.fn, inverse = options.inverse;