Situation:
A user is watching a page. Everytime someone mention him in that page, he receives two e-mails. One saying that the page was changed or commented, and other saying that he was mentioned. For users who use this features, it can be annoying.

Steps to reproduce:
If a user is already watching a page
1) Create a page as user A
2) User B watches this page (either by commenting or explictly adding themselves as a watcher)
3) User A adds a comment to the page mentioning (@userB) User B.

If the user is already watching a page and a task is assigned to them
1) Create a page as user A
2) User B watches the page
3) User A assigns a task to User B. User B now gets two emails (Assigned task, and a page mention)

Expected Result:
User B receives one e-mail (take a pick of choosing the comment or the mention)

Actual Result:
User B receives two e-mails (one for the mention, one for the comment)