Bug 13799 JAR exporter exports class files from output folder
There was a problem with the output folder not being detected as such.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/jarpackager/JarFileExportOperation.java
import org.eclipse.ui.IEditorPart;
import org.eclipse.ui.IFileEditorInput;
import org.eclipse.jdt.core.IJavaElement;
import org.eclipse.jdt.core.IJavaModelMarker;
import org.eclipse.jdt.core.IJavaProject;
import org.eclipse.jdt.core.IPackageFragment;
import org.eclipse.jdt.core.IPackageFragmentRoot;
import org.eclipse.jdt.core.JavaCore;
import org.eclipse.jdt.core.JavaModelException;
import org.eclipse.jdt.ui.jarpackager.IJarDescriptionWriter;
import org.eclipse.jdt.ui.jarpackager.IJarExportRunnable;
import org.eclipse.jdt.ui.jarpackager.JarPackageData;
import org.eclipse.jdt.ui.jarpackager.JarWriter;
import org.eclipse.jdt.internal.corext.util.JavaModelUtil;
import org.eclipse.jdt.internal.ui.JavaPlugin;
import org.eclipse.jdt.internal.ui.JavaStatusConstants;
import org.eclipse.jdt.internal.ui.util.BusyIndicatorRunnableContext;
/**
 * Operation for exporting a resource and its children to a new  JAR file.
 */
public class JarFileExportOperation implements IJarExportRunnable {
	private static final String COMPILER_SOURCE_FILE_ATTR = "org.eclipse.jdt.core.compiler.debug.sourceFile"; 
	private JarWriter fJarWriter;
	private JarPackageData fJarPackage;
	private JarPackageData[] fJarPackages;
	private IFile[] fDescriptionFiles;
	private Shell fParentShell;
	private Map fJavaNameToClassFilesMap;
	private IContainer fClassFilesMapContainer;
	private Set fExportedClassContainers;