sequential file creation should return location header

otherwise the client doesn't know where the sequential file is.

http://en.wikipedia.org/wiki/HTTP_location

```
curl "http://localhost:10000/?sequential" -XPOST -v
> POST /?sequential HTTP/1.1
> User-Agent: curl/7.32.0
> Host: localhost:10000
> Accept: */*
> 
< HTTP/1.1 200 OK
< Date: Sun, 07 Dec 2014 19:54:36 GMT
< Content-Type: text/html
< Content-Length: 0
< 
```