Improve network graph

### Before

* The commits is not ordered by commiter date.
* Not detecting an overlap of a line in some cases.

![network_graph_before](https://f.cloud.github.com/assets/72138/204367/74720946-8173-11e2-962c-761c69fa4d54.png)

### After

![network_graph_after](https://f.cloud.github.com/assets/72138/204368/77e54cf0-8173-11e2-8343-e51aaacb71b9.png)