Comments shouldn't be imported from auto-generated bug watches

When reporting bug 296707 I included the URL of a Trac ticket in the description. Appropriately, this did not get treated as a bug watch. But when I included the URLs of two other Trac tickets in a later comment in the same report, they were both inappropriately treated as bug watches. Launchpad then imported inappropriate comments from both of the Trac reports. This in turn means that when I try to delete one of the inappropriate bug watches, I get an oops (e.g. OOPS-1046D4100).

Just to add a little weirdness, the page in which I'm reporting this bug itself begins with six notifications, all of which say "The gobby-bugs #272 bug watch has been deleted", which isn't true.

My preferred fix to this bug, naturally, involves removing something: abolishing autogenerated bug watches altogether, in favor of on-the-fly project registration so that external bug reports can be associated with the real projects to which they belong. That's probably a fair bit of work though.

Another way of fixing it would be to make deleting a bug watch also delete any comments that were imported as a result of that bug watch.

Yet another way of fixing it would be to import external bug comments only for bug watches that were not autogenerated, and then to manually remove the inappropriately imported comments from bug 296707.