Bug 46805 prepare Compare for encoding support
I20031111 The Compare plugin only supports the global workspace encoding. It does not support encodings per file.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/compare/JavaHistoryAction.java
JavaHistoryAction(boolean modifiesFile) {
		fModifiesFile= modifiesFile;
	}
	
	ISelection getSelection() {
		return fSelection;
	}
		
	final IFile getFile(Object input) {
		
		ICompilationUnit cu= null;
		if (input instanceof ICompilationUnit)
			cu= (ICompilationUnit) input;
		else if (input instanceof IMember)
			cu= ((IMember)input).getCompilationUnit();
			
		if (cu == null || !cu.exists())
			return null;
			
		
		cu= JavaModelUtil.toOriginal(cu);
			
		
		IFile file= (IFile) cu.getResource();
		if (file != null && file.exists())
			return file;
		return null;
	}