* @param success GNUNET_SYSERR on failure (including timeout/queue drop)
* GNUNET_NO if content was already there
* GNUNET_YES (or other positive value) on success
* @param success GNUNET_SYSERR on failure (including timeout/queue drop)
* GNUNET_NO if content was already there
* GNUNET_YES (or other positive value) on success