/// @param fromURI File to download from vehicle, fully qualified path. May be in the format "mftp://[;comp=<id>]..." where the component id is specified.
/// If component id is not specified MAV_COMP_ID_AUTOPILOT1 is used.
/// @param toDir Local directory to download file to
/// @param filename (optional)
/// @param checksize (optional, default true) If true compare the filesize indicated in the open
/// response with the transmitted filesize. If false the transmission is tftp style
/// and the indicated filesize from MAVFTP fileopen response is ignored.
/// This is used for the APM parameterdownload where the filesize is wrong due to
/// a dynamic file creation on the vehicle.
/// @param fromCompId Component id of the component to download from. If fromCompId is MAV_COMP_ID_ALL, then MAV_COMP_ID_AUTOPILOT1 is used.
/// @param fromURI File to download from component, fully qualified path. May be in the format "mftp://[;comp=<id>]..." where the component id
/// is specified. If component id is not specified, then the id set via fromCompId is used.
/// @param toDir Local directory to download file to
/// @param filename (optional)
/// @param checksize (optional, default true) If true compare the filesize indicated in the open
/// response with the transmitted filesize. If false the transmission is tftp style
/// and the indicated filesize from MAVFTP fileopen response is ignored.
/// This is used for the APM parameter download where the filesize is wrong due to
/// a dynamic file creation on the vehicle.
/// @return true: download has started, false: error, no download