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
ElementTreeSelectionDialog dialog= new ElementTreeSelectionDialog(getShell(), lp, cp);
		dialog.setTitle(NewWizardMessages.getString("BuildPathsBlock.ChooseOutputFolderDialog.title")); 
		dialog.setValidator(validator);
		dialog.setMessage(NewWizardMessages.getString("BuildPathsBlock.ChooseOutputFolderDialog.description")); 
		dialog.addFilter(filter);
		dialog.setInput(fWorkspaceRoot);
		dialog.setInitialSelection(initSelection);
		
		if (dialog.open() == dialog.OK) {
			return (IContainer)dialog.getFirstResult();
		}
		return null;
	}
	
	
	
	private void tabChanged(Widget widget) {
		if (widget instanceof TabItem) {
			BuildPathBasePage newPage= (BuildPathBasePage) ((TabItem) widget).getData();
			if (fCurrPage != null) {
				List selection= fCurrPage.getSelection();
				if (!selection.isEmpty()) {
					newPage.setSelection(selection);
				}
			}
			fCurrPage= newPage;
		}
	}		
}