Merge https://github.com/documentcloud/underscore into unittests

underscore.js

@@ -170,7 +170,7 @@
   // **Reduce** builds up a single result from a list of values, aka `inject`,
   // or `foldl`. Delegates to **ECMAScript 5**'s native `reduce` if available.
   _.reduce = _.foldl = _.inject = function(obj, iterator, memo, context) {
-    var initial = memo !== void 0;
+    var initial = arguments.length > 2;
     if (obj == null) obj = [];
     if (nativeReduce && obj.reduce === nativeReduce) {
       if (context) iterator = _.bind(iterator, context);
@@ -184,20 +184,22 @@
         memo = iterator.call(context, memo, value, index, list);
       }
     });
-    if (!initial) throw new TypeError("Reduce of empty array with no initial value");
+    if (!initial) throw new TypeError('Reduce of empty array with no initial value');
     return memo;
   };
 
   // The right-associative version of reduce, also known as `foldr`.
   // Delegates to **ECMAScript 5**'s native `reduceRight` if available.
   _.reduceRight = _.foldr = function(obj, iterator, memo, context) {
+    var initial = arguments.length > 2;
     if (obj == null) obj = [];
     if (nativeReduceRight && obj.reduceRight === nativeReduceRight) {
       if (context) iterator = _.bind(iterator, context);
-      return memo !== void 0 ? obj.reduceRight(iterator, memo) : obj.reduceRight(iterator);
+      return initial ? obj.reduceRight(iterator, memo) : obj.reduceRight(iterator);
     }
-    var reversed = (_.isArray(obj) ? obj.slice() : _.toArray(obj)).reverse();
-    return _.reduce(reversed, iterator, memo, context);
+    var reversed = _.toArray(obj).reverse();
+    if (context && !initial) iterator = _.bind(iterator, context);
+    return initial ? _.reduce(reversed, iterator, memo, context) : _.reduce(reversed, iterator);
   };
 
   // Return the first value which passes a truth test. Aliased as `detect`.
@@ -388,7 +390,7 @@
     return (n != null) && !guard ? slice.call(array, 0, n) : array[0];
   };
 
-  // Returns everything but the last entry of the array. Especcialy useful on
+  // Returns everything but the last entry of the array. Especially useful on
   // the arguments object. Passing **n** will return all the values in
   // the array, excluding the last N. The **guard** check allows it to work with
   // `_.map`.