Fix compilation of examples with QStringBuilder

Fix compilation of examples with QStringBuilder

In sub-attack an interview, one can't make two implicit conversions at
once, so explicitly convert to the right type.

The change in the torrent example is required because of
https://codereview.qt-project.org/16168 (commit 9491272)
But in that case, using a QByteArray is better anyway.

Change-Id: Ieed22ac7f0d700d5ba5d1e70af3db4dd6c139c8f
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>