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
if (!canBeExported)
			return Collections.EMPTY_LIST.iterator();
		reportPossibleCompileProblems(file, hasErrors, hasWarnings, canBeExported);
		IContainer classContainer= outputContainer;
		if (pathInJar.segmentCount() > 1)
			classContainer= outputContainer.getFolder(pathInJar.removeLastSegments(1));
			
		if (fExportedClassContainers.contains(classContainer))
			return Collections.EMPTY_LIST.iterator();
			
		if (fClassFilesMapContainer == null || !fClassFilesMapContainer.equals(classContainer)) {
			fJavaNameToClassFilesMap= buildJavaToClassMap(classContainer);
			if (fJavaNameToClassFilesMap == null) {
				
				String msg= JarPackagerMessages.getFormattedString("JarFileExportOperation.missingSourceFileAttributeExportedAll", classContainer.getLocation().toFile()); 
				addWarning(msg, null);
				fExportedClassContainers.add(classContainer);
				return getClassesIn(classContainer);
			}
			fClassFilesMapContainer= classContainer;
		}
		ArrayList classFileList= (ArrayList)fJavaNameToClassFilesMap.get(file.getName());
		if (classFileList == null || classFileList.isEmpty()) {
			String msg= JarPackagerMessages.getFormattedString("JarFileExportOperation.classFileOnClasspathNotAccessible", file.getFullPath()); 
			throw new CoreException(new Status(IStatus.ERROR, JavaPlugin.getPluginId(), JavaStatusConstants.INTERNAL_ERROR, msg, null));
		}
		return classFileList.iterator();
	}
	private Iterator getClassesIn(IContainer classContainer) throws CoreException {
		IResource[] resources= classContainer.members();