Bug 9159 Classpath wizard should not complain when adding missing source folder
Build 20020125 - Define a project A with source folder 'src1'. - Go to the .classpath file and edit it to insert one extra line: <classpathentry kind="src" path="src2"/> below the line referring to first source folder: <classpathentry kind="src" path="src1"/>. - Now, try to add this missing source folder 'src2', it isn't allowed by the wizard, one has to add a basic folder instead. Note: It is not such an uncommon scenario, the classpath modification could simply occur by catching up with a shared classpath having one more source folder on it, and which is locally missing.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/BuildPathsBlock.java
IClasspathEntry[] classpath= new IClasspathEntry[nEntries];
		
		
		
		for (int i= 0; i < nEntries; i++) {
			CPListElement entry= ((CPListElement)classPathEntries.get(i));
			IResource res= entry.getResource();
			if ((res instanceof IFolder) && !res.exists()) {
				CoreUtility.createFolder((IFolder)res, true, true, null);
			}
			classpath[i]= entry.getClasspathEntry();
						
			
			URL javadocLocation= entry.getJavadocLocation();
			if (javadocLocation != null) {
				IPath path= entry.getPath();
				if (entry.getEntryKind() == IClasspathEntry.CPE_VARIABLE) {
					path= JavaCore.getResolvedVariablePath(path);
				}
				if (path != null) {
					JavaDocLocations.setLibraryJavadocLocation(path, javadocLocation);
				}
			}
		}	
		monitor.worked(1);
				
		fCurrJProject.setRawClasspath(classpath, outputLocation, new SubProgressMonitor(monitor, 7));		
	}
	private void removeOldClassfiles(IResource resource) throws CoreException {
		if (resource.isDerived() && "class".equals(resource.getFileExtension())) {