Do not create /tmp

Here's what I get without the patch:

```
 ** [out :: 185.10.48.88] mkdir: cannot create directory `/u/apps/application/releases/20130128174244/tmp'
 ** [out :: 185.10.48.88] : File exists
    command finished in 277ms
*** [deploy:update_code] rolling back
```

Apparently the `tmp` directory gets created somewhere before and it breaks the deployment.