Only ignore Status changed note emails if system, not if made by users.


Currently, if you make an issue comment that starts with the magic string:

    _Status changed to closed_

no notifications are generated.

After this PR they are, using the same mechanism that fixed this problem for `_mentioned in` notes, by first doing a `note.system` check.
I can't find the style guide reference to how to handle this indentation, but I don't like 3 spaces. I know it lines up all nicely but looks horrible with the `return true` on the following line. I'd almost opt for 4 spaces. What do you think?