one if we're upgrading from a version of Bugzilla before 4.0, and we figure this out now by checking the existence of bugs_activity.comment_id. r=LpSolit, a=mkanat git-svn-id: svn://10.0.0.236/branches/BUGZILLA-4_0-BRANCH@261455 18797224-902f-48f8-a5cc-f745e15eee43