Fix composer

From a fresh clone, when trying to run `phpunit` : 
> You must set up the project dependencies, run the following commands:
> wget http://getcomposer.org/composer.phar
> php composer.phar install --dev

When running `php composer.phar install --dev` :
> [RuntimeException]
> Your composer.lock was created before 2012-09-15, and is not supported anymore. Run "composer update" to generate a new one.

And finally, when `running php composer.phar update --dev` :
> Problem 1
> - The requested package zetacomponents/unit-test could not be found in any version, there may be a typo in the package name.
> 
> Potential causes:
>  The package is not available in a stable-enough version according to your minimum-stability setting

So here are 2 patches : the first to set `minimum-stability` to `dev`, the second updating composer.lock to be able to install the vendors.