They never should have been using the config parameter directly, but the
hash returned form the revision() method.

Added drush method for calling drush commands as tasks, some other cleanups as well. Still some messy bits.

* Switched to using symfony's autoloader, moved namespaces around to fit.
* Simplified before/after tasks, now just uses drush options.
* Added dependency classes.

Methods now use docblock annotations to declare themselves as commands. Also swapped out drush_shell_exec for an async version of _drush_proc_open.

* The new DrushCommand class added with the intention of eventually going upstream.
* Before and after tasks added using closures in the config file, inspired by phake.