reorganization, everything based on Tree2 now --HG-- rename : src/HOL/Data_Structures/Set2_BST2_Join.thy => src/HOL/Data_Structures/Set2_Join.thy rename : src/HOL/Data_Structures/Set2_BST2_Join_RBT.thy => src/HOL/Data_Structures/Set2_Join_RBT.thy