Check for '/r/' and add it if it is not included

This code does a quick check for '/r/' on the front of the subreddit
name. If it is not included, then it is added automatically. This is not
done for the special case '/', which coresponds to the front page.
Merge pull request #30 from DSMan195276/prepend-on-subreddit

Check for '/r/' and add it if it is not included