[QA failed] play nicely if we get a old post request when adding comment

**CR** : :white_check_mark: 

**QA** : :x:
> *test core functionality of feature:*
> :white_check_mark: comment in a discussion
> :white_check_mark: posted with JS disabled
> :x: when DiscussionService fails, page doesn't reload, so no flash..... user won't know what happened

> *test functionality adjacent to this feature:*
> :question: - can't think of any relevant...

> :ok: logged out functionality - NA

> :question: test in IE 8,9 
> :ok: test in production environment - NA I hope 

**CO signoff** : :question:
**DO signoff** : :question:

**PO signoff** : :question:

---
useful symbols :white_check_mark: :ok: :x: :question: