The gedit indent lines plugin was removed. I then looked at the documentation with F1, but the Shortcut keys manual page had a parsing error and yelp didn't want to show me more then the first few keys. I then turned to the internet and found nothing.
Turns out this is one of those: it's to easy, so it doesn't need any documentation cases. The indent key is now TAB instead of Ctrl+M and Ctrl+m. So now you can use TAB and Shift+TAB to indent and un-indent your selection in gedit.