Altering "varargs" (remove|retain)AllKeys in Jaggregate

As with the analogous jaggregate.Collection methods, I've modified the removeAllKeys( K... ) and retainAllKeys( K... ) methods to have parameter list ( K[] ), and added overloads that have parameter list ( K, K... ), to avoid big confusion when programs hand zero args to the varargs versions of the method. This and the previous modifications will show up in version 2.