Bug 86135 Make use of new IResource#revertModificationStamp(long) API
org.eclipse.ltk.core.refactoring/src/org/eclipse/ltk/core/refactoring/UndoTextFileChange.java
if (pm == null)
			pm= new NullProgressMonitor();
		pm.beginTask("", 1); 
		fValidationState= BufferValidationState.create(fFile);
		ITextFileBuffer buffer= FileBuffers.getTextFileBufferManager().getTextFileBuffer(fFile.getFullPath());
		fDirty= buffer != null && buffer.isDirty();
		pm.worked(1);
	}
	
	/**
	 * {@inheritDoc}
	 */
	public RefactoringStatus isValid(IProgressMonitor pm) throws CoreException {
		if (pm == null)
			pm= new NullProgressMonitor();
		pm.beginTask("", 1); 
		RefactoringStatus result= fValidationState.isValid();
		pm.worked(1);
		return result;
	}
	
	/**
	 * {@inheritDoc}
	 */
	public Change perform(IProgressMonitor pm) throws CoreException {
		if (pm == null)
			pm= new NullProgressMonitor();
		ITextFileBufferManager manager= FileBuffers.getTextFileBufferManager();
		pm.beginTask("", 2); 
		ITextFileBuffer buffer= null;