Bug 141192 [Viewers] Javadoc change about multiple equal elements in StructuredViewer and AbstractTreeViewer
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/StructuredViewer.java
* IMPORTANT: This method was introduced in 3.2. If a reference to this viewer object 
     * is passed to clients who call <code>getSorter()<code>, null may be returned from
     * from that method even though the viewer is sorting its elements using the
     * viewer's comparator.
     * </p>
	 * 
	 * @param comparator a viewer comparator, or <code>null</code> if none
     *
     * @since 3.2
	 */
	public void setComparator(ViewerComparator comparator){
		if (this.sorter != comparator){
			this.sorter = comparator;
			refresh();
		}
	}
	
	/**
	 * Configures whether this structured viewer uses an internal hash table to
	 * speeds up the mapping between elements and SWT items. This must be called
	 * before the viewer is given an input (via <code>setInput</code>).
	 * 
	 * @param enable
	 *            <code>true</code> to enable hash lookup, and
	 *            <code>false</code> to disable it
	 */
	public void setUseHashlookup(boolean enable) {
		Assert.isTrue(getInput() == null,
				"Can only enable the hash look up before input has been set");
		if (enable) {