Asynchronously queries the this for a FileInfo.
callback will be called with a AsyncResult which
can be used to finish the operation with query_info_async.end.
For the synchronous version of this function, see query_info .
a file attribute query string.
the I/O priority of the request
optional Cancellable object, null to ignore.
callback to call when the request is satisfied
the data to pass to callback function