Use the configured paths for Porpel and Phing

This PR let the end user to configure the paths to Propel and Phing in the configuration file. 

I have a symfony 1.4 project wich uses Propel and a Symfony 2 one that will use the same model. I wanted to tell Syfmony 2 to use the version of Propel installed in the symfony 1.4 to avoid autoloading issues.