Remove ability to comment '+1' on issues

Sometimes an issue gains a lot of attention, and people simply comment '+1' to show they would like the feature/fix to be implemented. However, this sends out a notification to all watchers on the current issue, to the annoyance of everyone. Often times there will be pleading to stop, which usually has little effect. This is especially bad on older issues which have hundreds of watchers.

See for example here, and here.

I would suggest some automated moderation here. If a user goes to comment with only the text '+1' (or similar potentially), instead we should intercept the user when they attempt to submit their comment, and tell them to vote or watch the issue instead.