Drush ensure branch command should not update branch if there are no changes

I think that the Drush command that makes sure a branch/project exists needs to be a bit more careful. It should only update the branch in the database if the new information is different from the existing information.

The reason this is important is that if a branch has been updated, the parse jobs in the queue for that branch are invalidated, and also it is forced to have a full scan at the next cron run. So if someone is using this drush command to (outside of the API module) maintain a large list of projects/branches, they might have trouble with the parse queue.