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
public void changeControlPressed(DialogField field) {
			buildPathChangeControlPressed(field);
		}
		
		
		public void dialogFieldChanged(DialogField field) {
			buildPathDialogFieldChanged(field);
		}
	}
	
	private void buildPathChangeControlPressed(DialogField field) {
		if (field == fBuildPathDialogField) {
			IContainer container= chooseContainer();
			if (container != null) {
				fBuildPathDialogField.setText(container.getFullPath().toString());
			}
		}
	}
	
	private void buildPathDialogFieldChanged(DialogField field) {
		if (field == fClassPathList) {
			updateClassPathStatus();
			updateBuildPathStatus();
		} else if (field == fBuildPathDialogField) {
			updateBuildPathStatus();