Backport is a fix vs added a feature (or whatever):

 * Find "Bug" footer
 * It's a bugfix if the phab task has a subtype of
   * Error
   * Bug

Problems/limitations with this approach:

 * When were the "bug/error"/task subtypes introduced to phab
 * When did we start using them consistantly
 * Do we use these subtypes consistantly now?
 * This will undercount actual problems

What's neat:

 * Find most backported to files:
   `select filename, count(*) as seen from bug_file group by filename
   order by seen desc limit 10;`

What's hard:

 * The relationships between trains, bugs, and patches is hard to model.
   To find bugs and patches for each train the query is a doozy:
   `select version, b.link, p.link
   from train t
   join bug_train bt on bt.train_id = t.id
   join bug b on bt.bug_id = b.id
   join bug_bug_patch bbp on bbp.bug_id = b.id
   join bug_patch p on p.id = bbp.bug_patch_id and p.train_id = t.id;`