Bug 120544 [build path] Editing external source folder does not persist
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/CPListElement.java
public void setLinkTarget(IPath linkTarget) {
		fLinkTarget= linkTarget;
	}
	public void setPath(IPath path) {
		fCachedEntry= null;
		fPath= path;
	}
	public static void insert(CPListElement element, List cpList) {
		int length= cpList.size();
		CPListElement[] elements= (CPListElement[])cpList.toArray(new CPListElement[length]);
		int i= 0;
		while (i < length && elements[i].getEntryKind() != element.getEntryKind()) {
			i++;
		}
		if (i < length) {
			i++;
			while (i < length && elements[i].getEntryKind() == element.getEntryKind()) {
				i++;
			}
			cpList.add(i, element);
			return;
		}
		
		switch (element.getEntryKind()) {
		case IClasspathEntry.CPE_SOURCE:
			cpList.add(0, element);
			break;
		case IClasspathEntry.CPE_CONTAINER:
		case IClasspathEntry.CPE_LIBRARY:
		case IClasspathEntry.CPE_PROJECT: