Failure to strip replies from emails with parents lacking quote '>' char, e.g. Yahoo Mail.

As an example email body:

```
Here's a reply

On Tuesday, February 10, 2015 4:25 PM, TestAccount wrote:

And here's the parent
```

parse_reply() isn't able to separate the reply from the parent in this case, it appears because the parent is lacking '>' characters in front. I would have thought this case unusual, but it seems Yahoo mail uses this style by default. Has anyone gotten parse_reply to work with Yahoo mail replies?

Start by reproducing the supplied Yahoo Mail-style body with parse_reply and inspect how the reply and parent are separated when the parent lacks leading quote characters. Done means the example reliably returns the reply separately from the parent content; the issue does not name a specific file or test to run.

索引モデルが issue の本文から書いたものです。