Private Messaging - Email notifications for follow-up replies within same thread

[davidtcarson]

Pre BP 1.2, private message recipients would receive an email notification every time a new private message was sent to them, whether that private message was a 'new/initial' message or whether that private message was a 'follow-up' message within an existing private message conversation.

In BP 1.2, it seems that private message recipients will only receive email notifications for 'new/initial' messages (the first message and the first reply trigger email notifications). Follow-up messages between users for an existing private message conversation will not trigger email notifications.

I've tested this both with my own install and on testbp.org. I'll post a patch if I can.

[apeatling]

(In [2651]) Fixes #1895