Bug 120544 [build path] Editing external source folder does not persist
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/BuildPathsBlock.java
* classpath entries of the existing project
	 */	
	public void init(IJavaProject jproject, IPath outputLocation, IClasspathEntry[] classpathEntries) {
		fCurrJProject= jproject;
		boolean projectExists= false;
		List newClassPath= null;
		IProject project= fCurrJProject.getProject();
		projectExists= (project.exists() && project.getFile(".classpath").exists()); 
		if  (projectExists) {
			if (outputLocation == null) {
				outputLocation=  fCurrJProject.readOutputLocation();
			}
			if (classpathEntries == null) {
				classpathEntries=  fCurrJProject.readRawClasspath();
			}
		}
		if (outputLocation == null) {
			outputLocation= getDefaultBuildPath(jproject);
		}			
		if (classpathEntries != null) {
			newClassPath= getExistingEntries(classpathEntries);
		}
		if (newClassPath == null) {
			newClassPath= getDefaultClassPath(jproject);
		}
		
		List exportedEntries = new ArrayList();
		for (int i= 0; i < newClassPath.size(); i++) {
			CPListElement curr= (CPListElement) newClassPath.get(i);
			if (curr.isExported() || curr.getEntryKind() == IClasspathEntry.CPE_SOURCE) {