Registering provider package namespace in register()

Lets the config repository know about the 'laravel-doctrine' package config namespace earlier.
We have code that tries to get <code>$config->get('laravel-doctrine::doctrine.metadata')</code> before the service provider's boot() method is called. This is currently a problem because the config repository doesn't know about the laravel-doctrine package until a call to <code>$this->package('laravel-doctrine')</code> is called in the boot() method.