Replacement of built-in apt_repository.

It is a rewritten version of apt_repository. I has some fixes for initial version's problems:

1. Debian Squeeze is supported out of box now.

2. deb-src will not be added implicitly.

3. If a source had beed added it must be able to remove it. If you will try this:
```
apt_repository: repo='deb http://ppa.launchpad.net/nginx/stable/ubuntu raring main'
apt_repository: repo='deb http://ppa.launchpad.net/nginx/stable/ubuntu raring additional'
apt_repository: repo='deb http://ppa.launchpad.net/nginx/stable/ubuntu raring additional' state=absent
```

You will have source ``deb http://ppa.launchpad.net/nginx/stable/ubuntu raring main additional`` in the source list, not any of strings you used in a playbook.


This module has some features may cause not-smooth migration:
1. it uses AtomicFile instead of backup files;
2. if supports PPA repositories only for Ubuntu target machines to prevent failures on plain Debian ones;
3. it requires repository type to be explicitly specified ("deb http://....", or "deb-src http://...")