Catching failed downloads

```
Fetching 'http://www.libsdl.org/projects/SDL_image/release/SDL_image-1.2.10.tar.gz'...
read timeout at /usr/lib/perl5/vendor_perl/5.10/LWP/Protocol/http.pm line 426. at /usr/lib/perl5/vendor_perl/5.10/LWP/UserAgent.pm line 844.
```

We should catch this and try the 2nd url.
