Added --pretty=oneline to `git log`

On my laptop (mac os X 10.8.4, git 1.8.3.3) the result of `git log --topo-order --left-right ${current_commit_hash}...${upstream} ` is something like this :

```
commit < 2b08f527038d1464ae03098ace6bb4b6efd44c69
Author: fcamblor <fcamblor@xxxx.com>
Date:   Wed Sep 11 17:49:24 2013 +0200

    An empty commit
```

So the `grep` command doesn't count anything here.
I think you're missing some `--pretty=oneline` argument here (maybe defaulted in your ~/.gitconfig file ?)

Wondering if `number_of_logs` variable should be affected too, WDYT ?