Prevent the rss from containing incomplete textile or markdown for links or images

Hi Gavin,

I had this issue on the rss feed of [my blog](https://www.mes-courses.fr/blog/posts.rss), for example, with textile, I got things like that in the post :

```
“!https://dl.dropbox.com/u/206938/mes-courses.fr/images/articles/visite-a-l-aquarium-de-paris/…
```

What do you think about it ?
Thanks,