Bug 153993 [Viewers] Common Baseclass for Tree/TableEditorImpl
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/TreeEditorImpl.java
cellEditorListener = new ICellEditorListener() {
            public void editorValueChanged(boolean oldValidState,
                    boolean newValidState) {
                
            }
            public void cancelEditor() {
                TreeEditorImpl.this.cancelEditing();
            }
            public void applyEditorValue() {
                TreeEditorImpl.this.applyEditorValue();
            }
        };
    }
    /**
     * Return whether or not there is an active cell editor.
     * @return boolean <code>true</code> if there is an active cell editor; otherwise
     * <code>false</code> is returned.
     */
    public boolean isCellEditorActive() {
        return cellEditor != null;
    }
    /**
     * Saves the value of the currently active cell editor,
     * by delegating to the cell modifier.
     */
    private void saveEditorValue(CellEditor cellEditor, Item treeItem) {
    	ViewerColumn part = viewer.getViewerColumn(columnNumber);
    	
    	if( part != null && part.getEditingSupport() != null ) {
        	part.getEditingSupport().setValue(treeItem.getData(), cellEditor.getValue());