Comment shown in activity log but missing from bug page

Bug 88020 and bug 86888 don't demonstrate any problem with the activity log itself. Comments are displayed in the activity log only if they were made while changing the status of a bug; in that case they overwrite a "status explanation" field, which I mistakenly proposed a long time ago and which is now hidden but not properly removed (reported as bug 88545). Daniel Holbach's comments in those two bug reports were not made while changing the status, and they are therefore not shown in the activity log. (In the long term this should be solved by interleaving the activity with the comments on the bug page itself, bug 807.)

However, bug 88442 does demonstrate a problem in that Andrew Mitchell's "+1" comment shown in the activity log is not shown in the bug report.

The underlying problem is that our anti-duplicate-comment code assumed it was a duplicated comment. I've added a check to that code to only consider duplicated comments from the same user. If they're identical but from different users, it should be displayed. Sending to pqm.