* FIX: Email Send post has already been taken error
Adding a failing test first before coming up with a good solution.
Related: 357011eb3b
The above commit changed
```
PostReplyKey.find_or_create_by_safe!
```
to
```
PostReplyKey.create_or_find_by!
```
But I don't think it is working as a 1-1 replacement because of the
`Validation failed: Post has already been taken` error we are receiving
with this change. Also we need to make sure we don't re-introduce any
concurrency issues.
Reported: https://meta.discourse.org/t/224706/13
* Remove rails unique constraint and rely on db index
I believe this is what is causing `create_or_find_by!` to fail. Because
we have a unique constraint in the db I think we can remove this rails
unique constraint?
* clean up spec wording
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
