use fileinfo object in search results

fixes log entries like:
```json
{"reqId":"53bd3a9247c78","app":"PHP","message":"Argument 1 passed to OC\\Search\\Result\\File::__construct() must be of the type array, object given, called in \/home\/jfd\/Repositories\/oc\/core\/lib\/private\/
search\/provider\/file.php on line 56 and defined at \/home\/jfd\/Repositories\/oc\/core\/lib\/private\/search\/result\/file.php#68","level":0,"time":"2014-07-09T12:50:26+00:00","method":"GET","url":"\/core\/ind
ex.php\/search\/ajax\/search.php?query=baz"}
```
@icewind1991 @DeepDiver1975 @PVince81 easy to reproduce: just search for a file
No, getRelativePath will get sth like `/admin/foo/bar/Neue Textdatei 3.txt` and the `OC\Files\Node\Folder` object returned by `\OC::$server->getUserFolder()` has its path set to `/admin/files`. As a result the folders getRelativePath() will throw a `NotFoundException`.