Commons-lang StringUtils head, tail and indexOfNth (with patch)

Hello commons developers,
I would like to propose the addition of these four methods to StringUtils class:

public static String head(final String str, int lines)
public static String tail(String str, int lines)
public static int indexOfNth(String str, String searchStr, int occurrence)
public static int lastIndexOfNth(String str, String searchStr, int occurrence)