Only create database backup after X updates

Great module.

I found myself upgrading some databases with huge datasets and hundreds of modules. This did all of the work, but it was taking forever to enable all of the modules since it did a backup after every module enabled. Considering that there were hardly any issues during the upgrade, this made things take a long time. In order to overcome the issue, I wrote a patch that would allow me to pass a parameter to only backup after X modules are enabled. Here's how to use it:

drush @d6 sup @d7 --backup-interval=5
The backup will run after every 5 modules are enabled in this case. Turned hours of upgrade time into about an hour. Contributing back in hopes that it goes in to the module or else someone else finds it useful.