Add diff support to apt_repository module
Add diff support to apt_repository module

The returned list of diffs aims to simulate how a file system diff would
look before and after writing the sources list files.

![screenshot](http://i.imgur.com/dH6QXtY.png)

n.b. Ternary conditional  is due to failing integration test for
python 2.4

thaim/ansible,thaim/ansible