Drush integration use wrong machine name for names with underscore

When we use drush integration to create subtheme with '_' or '-' in name (eg mother_ship) we get files with 'mother-ship' string in every place where machine name is expected:

• mother-ship.info file
• function mother-ship_some_hook()
• etc.

It's obviously wrong, and it's because drupal_clean_css_identifier was used for cleaning the name.

I've noticed that in this issue doesn't exists in Zen. I've copied their solution for names, and I worked as expected.

Patch on the way.