Bug 120544 [build path] Editing external source folder does not persist
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/SourceContainerWorkbookPage.java
int nFolders= fFoldersList.getSize();
				for (int i= 0; i < nFolders; i++) {
					CPListElement cpe= (CPListElement) fFoldersList.getElement(i);
					cpe.setAttribute(CPListElement.OUTPUT, null);
				}
			}
			fFoldersList.refresh();
		} else if (field == fFoldersList) {
			updateClasspathList();
		}
	}	
	
		
	private void updateClasspathList() {
		List srcelements= fFoldersList.getElements();
		
		List cpelements= fClassPathList.getElements();
		int nEntries= cpelements.size();
		
		int lastRemovePos= nEntries;
		int afterLastSourcePos= 0;
		for (int i= nEntries - 1; i >= 0; i--) {
			CPListElement cpe= (CPListElement)cpelements.get(i);
			int kind= cpe.getEntryKind();
			if (isEntryKind(kind)) {
				if (!srcelements.remove(cpe)) {
					cpelements.remove(i);
					lastRemovePos= i;
				} else if (lastRemovePos == nEntries) {
					afterLastSourcePos= i + 1;