Bug 93287 LTK Core Refactoring triggered on shutdown of JavaPlugin
org.eclipse.ltk.core.refactoring/src/org/eclipse/ltk/core/refactoring/RefactoringCore.java
private static IUndoManager fgUndoManager= null;
	private static IValidationCheckResultQueryFactory fQueryFactory= new DefaultQueryFactory();
	private static class NullQuery implements IValidationCheckResultQuery {
		public boolean proceed(RefactoringStatus status) {
			return true;
		}
		public void stopped(RefactoringStatus status) {
			
		}
	}
	
	private static class DefaultQueryFactory implements IValidationCheckResultQueryFactory {
		public IValidationCheckResultQuery create(IAdaptable context) {
			return new NullQuery();
		}
	}
	
	private RefactoringCore() {
		
	}
	
	/**
	 * Returns the singleton undo manager for the refactoring undo