([NSDictionary +_setMutableConcreteClass:]): New method.
([NSDictionary +_concreteClass]): New method.
([NSDictionary +_mutableConcreteClass]): New method.
([NSDictionary +initialize]): New method.
(NSDictionary_concrete_class, NSMutableDictionary_concrete_class): New
static variables.
([NSDictionary -copyWithZone:]): Make a deep copy to conform to spec;
it was a shallow copy.
git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/base/trunk@475 72102866-910b-0410-8b05-ffd578937521
