Add a third "context" argument to Backbone.Event.Bind which, when passed, will bind the callback to the provided context.

Example:

	Backbone.Event.Bind('event', this.event, this);

Before this commit the way to do this was as follows:

	Backbone.Event.Bind('event', _.bind(this.event, this));

backbone.js

@@ -68,10 +68,10 @@
 
     // Bind an event, specified by a string name, `ev`, to a `callback` function.
     // Passing `"all"` will bind the callback to all events fired.
-    bind : function(ev, callback) {
+    bind : function(ev, callback, context) {
       var calls = this._callbacks || (this._callbacks = {});
       var list  = calls[ev] || (calls[ev] = []);
-      list.push(callback);
+      list.push([callback, context]);
       return this;
     },
 
@@ -89,7 +89,7 @@
           var list = calls[ev];
           if (!list) return this;
           for (var i = 0, l = list.length; i < l; i++) {
-            if (callback === list[i]) {
+            if (list[i] && callback === list[i][0]) {
               list[i] = null;
               break;
             }
@@ -114,7 +114,7 @@
               list.splice(i, 1); i--; l--;
             } else {
               args = both ? Array.prototype.slice.call(arguments, 1) : arguments;
-              callback.apply(this, args);
+              callback[0].apply(callback[1] || this, args);
             }
           }
         }

test/events.js

@@ -66,5 +66,21 @@ $(document).ready(function() {
     equals(obj.counterA, 1, 'counterA should have only been incremented once.');
     equals(obj.counterB, 1, 'counterB should have only been incremented once.');
   });
+  
+  test("Events: bind a callback with a supplied context", function () {
+    expect(1);
+    
+    var TestClass = function () { return this; }
+    TestClass.prototype.assertTrue = function () {
+      ok(true, '`this` was bound to the callback')
+    };
+    
+    var obj = _.extend({},Backbone.Events);
+    
+    obj.bind('event', function () { this.assertTrue(); }, (new TestClass));
+    
+    obj.trigger('event');
+    
+  });
 
 });