email reply notification should include notice replied to

Link to context is great, was added in 1770 fix.

For long conversations, it can still be hard to discern which notice is being replied to. For this, and providing as much useful info in email as possible, it would be nice if email reply notification also included:

* text of notice being replied to
* link to notice being replied to

Idea for this issue from zotz http://identi.ca/notice/87974128