systemManifest.set(header, null); systemManifest.set(header, newValue);
systemManifest.set(header, newValue, true);
	private void appendManifestValue(Headers systemManifest, String header, String append) {		String newValue = (String) systemManifest.get(header);		if (newValue == null) {			newValue = append;		} else {			newValue += "," + append; //$NON-NLS-1$		}		systemManifest.set(header, null);		systemManifest.set(header, newValue);	}