Upgrade to Composer 1.0.0-alpha9

The latest alpha of Composer is seriously faster at resolving dependencies which improves composer install / update. On one project this brought composer update from running in several minutes to 10 seconds or so.

This patch is simply running composer update along with rebuilding composer.drush.json as shown in the README.

For anyone wanting to upgrade locally, it's probably easier to use composer to update instead of applying the patch. Just modify composer.json in ~/.drush/composer to point to alpha9, and run composer update.