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
`FileInfo::getPath()` will always return an absolute path (starting with `/$user/files`)