make toArray return a clone in case of an array

In combination with backbone this makes coll.toArray() return an array
instead of just returning coll.models, enabling
coll.remove(coll.toArray()) whithout failing half way through.

test/collections.js

@@ -197,6 +197,9 @@ $(document).ready(function() {
   test('collections: toArray', function() {
     ok(!_.isArray(arguments), 'arguments object is not an array');
     ok(_.isArray(_.toArray(arguments)), 'arguments object converted into array');
+    var a = [1,2,3];
+    ok(_.toArray(a) !== a, 'array is cloned');
+    equals(_.toArray(a).join(', '), '1, 2, 3', 'cloned array contains same elements');
 
     var numbers = _.toArray({one : 1, two : 2, three : 3});
     equals(numbers.join(', '), '1, 2, 3', 'object flattened into array');

underscore.js

@@ -278,7 +278,7 @@
   _.toArray = function(iterable) {
     if (!iterable)                return [];
     if (iterable.toArray)         return iterable.toArray();
-    if (_.isArray(iterable))      return iterable;
+    if (_.isArray(iterable))      return slice.call(iterable);
     if (_.isArguments(iterable))  return slice.call(iterable);
     return _.values(iterable);
   };