Allow drush pm to append module version data to .info files

When a site is built using Drush, and then handed off to a developer who doesn't use Drush, or deployed to a host that doesn't have CVS enabled, the lack of version data in the .info files can create problems.

The attached patch appends relevant data to the .info file after cvs checkout or update in a similar manner to the Drupal package manager.

I'm not sure if this is the right way to go, but it's a first attempt.