Cloning the output from getExcludeFieldNames, adjusting the code to use the attribute directly so it doesn't pay the clone() cost every time and changing the attribute from private to protected to let subclasses retain the ability to modify the field names (if that is why a getExcludeFieldNames method existed). Document in LANG-489
commons/proper/lang/trunk/src/java/org/apache/commons/lang/builder/ReflectionToStringBuilder.java