Bug 127723 refactoring history: warn when replacing a jar with an older version
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/jarimport/JarImportWizardPage.java
handleJarFileChanged();
		if (isPageComplete())
			handlePackageFragmentRootChanged();
		if (fImportWizard && !fTreeViewer.getControl().isEnabled())
			setErrorMessage(JarImportMessages.JarImportWizardPage_no_jar_files);
		getContainer().updateButtons();
	}
	/**
	 * Handles the jar file changed event.
	 */
	protected void handleJarFileChanged() {
		if (fLocationField != null) {
			final String path= fLocationField.getText();
			if ("".equals(path)) { 
				setErrorMessage(JarImportMessages.JarImportWizardPage_empty_location);
				setPageComplete(false);
				return;
			} else {
				final File file= new File(path);
				if (!file.exists()) {
					setErrorMessage(JarImportMessages.JarImportWizardPage_invalid_location);
					setPageComplete(false);
					return;
				}
				ZipFile zip= null;
				try {
					zip= new ZipFile(file, ZipFile.OPEN_READ);
				} catch (IOException exception) {
					setErrorMessage(JarImportMessages.JarImportWizardPage_invalid_location);
					setPageComplete(false);