Bug 289599 [Preferences] PreferenceStore.setToDefault fires redundant PropertyChangeEvents
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferenceStore.java
* or <code>setValue</code>; initially <code>false</code>.
	 */
	private boolean dirty = false;
	/**
	 * The file name used by the <code>load</code> method to load a property
	 * file. This filename is used to save the properties file when
	 * <code>save</code> is called.
	 */
	private String filename;
	/**
	 * Creates an empty preference store.
	 * <p>
	 * Use the methods <code>load(InputStream)</code> and
	 * <code>save(InputStream)</code> to load and store this preference store.
	 * </p>
	 * 
	 * @see #load(InputStream)
	 * @see #save(OutputStream, String)
	 */
	public PreferenceStore() {
		defaultProperties = new Properties();
		properties = new Properties(defaultProperties);
	}
	/**
	 * Creates an empty preference store that loads from and saves to the a
	 * file.
	 * <p>
	 * Use the methods <code>load()</code> and <code>save()</code> to load
	 * and store this preference store.
	 * </p>