Code review comment for lp:~intellectronica/launchpad/update-max-heat

When BugTasks are created or retargetted, the maximums need to be recalculated too (both for the old target and the new target). I don't think we delete BugTasks so we don't need to cope with that case.

The Distribution.max_bug_heat needs to include bugs linked to a distroseries (Only one of BugTask.distroseries and BugTask.distribution can be set).