Nested 'then' not working properly. Fixed

In previous version nested then didn't work at expected:

```javascript
context.load("templates/home.template"
			).then(function(){
				context.log("1");
				this.load("templates/home.template"
				).then(function(){
					context.log("2");
					this.load("templates/home.template"
					).then(function(){
						context.log("3");
						this.load("templates/home.template"
						).then(function(){
							context.log("3a");
						}).then(function(){
							context.log("3b");
						});
					});
				}).then(function(){
					context.log("4");
				});
			}).then(function(){
				context.log("5");
			}).then(function(){
				context.log("6");
				this.load("templates/home.template"
				).then(function(){
					context.log("7");
					this.load("templates/home.template"
					).then(function(){
						context.log("8");
					});
				}).then(function(){
					context.log("9");
				});				
			});
```
returns: 

[Fri Jun 07 2013 16:47:28 GMT+0200 (CEST)] 1 sammy.js:97
[Fri Jun 07 2013 16:47:28 GMT+0200 (CEST)] 5 sammy.js:97
[Fri Jun 07 2013 16:47:28 GMT+0200 (CEST)] 6 sammy.js:97
[Fri Jun 07 2013 16:47:28 GMT+0200 (CEST)] 2 sammy.js:97
[Fri Jun 07 2013 16:47:28 GMT+0200 (CEST)] 4 sammy.js:97
[Fri Jun 07 2013 16:47:28 GMT+0200 (CEST)] 7 sammy.js:97
[Fri Jun 07 2013 16:47:28 GMT+0200 (CEST)] 9 sammy.js:97
[Fri Jun 07 2013 16:47:39 GMT+0200 (CEST)] 3 sammy.js:97
[Fri Jun 07 2013 16:47:39 GMT+0200 (CEST)] 8 sammy.js:97
[Fri Jun 07 2013 16:47:39 GMT+0200 (CEST)] 3a sammy.js:97
[Fri Jun 07 2013 16:47:39 GMT+0200 (CEST)] 3b sammy.js:97

With the change it outputs what we expect:

[Fri Jun 07 2013 16:48:41 GMT+0200 (CEST)] 1 sammy.js:97
[Fri Jun 07 2013 16:48:41 GMT+0200 (CEST)] 2 sammy.js:97
[Fri Jun 07 2013 16:48:41 GMT+0200 (CEST)] 3 sammy.js:97
[Fri Jun 07 2013 16:48:41 GMT+0200 (CEST)] 3a sammy.js:97
[Fri Jun 07 2013 16:48:41 GMT+0200 (CEST)] 3b sammy.js:97
[Fri Jun 07 2013 16:48:41 GMT+0200 (CEST)] 4 sammy.js:97
[Fri Jun 07 2013 16:48:41 GMT+0200 (CEST)] 5 sammy.js:97
[Fri Jun 07 2013 16:48:41 GMT+0200 (CEST)] 6 sammy.js:97
[Fri Jun 07 2013 16:48:41 GMT+0200 (CEST)] 7 sammy.js:97
[Fri Jun 07 2013 16:48:41 GMT+0200 (CEST)] 8 sammy.js:97
[Fri Jun 07 2013 16:48:41 GMT+0200 (CEST)] 9 sammy.js:97