Bug 81078 [preferences] Restore Defaults duplicates list entries
I200412142000 Restore Defaults on Java > Editor > Appearance duplicates the "Appearance color options" entries.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/preferences/AbstractConfigurationBlock.java
/**
	 * Use as follows:
	 * 
	 * <pre>
	 * SectionManager manager= new SectionManager();
	 * Composite composite= manager.createSectionComposite(parent);
	 * 
	 * Composite xSection= manager.createSection("section X"));
	 * xSection.setLayout(new FillLayout());
	 * new Button(xSection, SWT.PUSH); // add controls to section..
	 * 
	 * [...]
	 * 
	 * return composite; // return main composite
	 * </pre>
	 */
	protected final class SectionManager {
		
		private static final String __NONE= "__none"; 
		private Set fSections= new HashSet();
		private boolean fIsBeingManaged= false;
		private ExpansionAdapter fListener= new ExpansionAdapter() {
			public void expansionStateChanged(ExpansionEvent e) {
				ExpandableComposite source= (ExpandableComposite) e.getSource();
				updateSectionStyle(source);